doc: update CONTRIBUTING.md (#2530)

* doc: update CONTRIBUTING.md

Remove bunch of old/stale text, but add a section (and clarify) using
issues to describe a future PR and that those need to be small (if you
want it merged faster)
Signed-off-by: Miek Gieben <miek@miek.nl>

* Update CONTRIBUTING.md
Co-Authored-By: miekg <miek@miek.nl>

CONTRIBUTING.md

 # Contributing to CoreDNS
 
-Welcome! Our community focuses on helping others and making CoreDNS the best it
-can be. We gladly accept contributions and encourage you to get involved!
+Welcome! Our community focuses on helping others and making CoreDNS the best it can be. We gladly
+accept contributions and encourage you to get involved!
 
-## Bug reports
+## Bug Reports
 
-First, please [search this repository](https://github.com/coredns/coredns/search?q=&type=Issues&utf8=%E2%9C%93)
-with a variety of keywords to ensure your bug is not already reported.
+First, please [search this
+repository](https://github.com/coredns/coredns/search?q=&type=Issues&utf8=%E2%9C%93) with a variety
+of keywords to ensure your bug is not already reported.
 
-If not, [open an issue](https://github.com/coredns/coredns/issues) and answer the
-questions so we can understand and reproduce the problematic behavior.
+If not, [open an issue](https://github.com/coredns/coredns/issues) and answer the questions so we
+can understand and reproduce the problematic behavior.
 
-The burden is on you to convince us that it is actually a bug in CoreDNS. This is
-easiest to do when you write clear, concise instructions so we can reproduce
-the behavior (even if it seems obvious). The more detailed and specific you are,
-the faster we will be able to help you. Check out
-[How to Report Bugs Effectively](http://www.chiark.greenend.org.uk/~sgtatham/bugs.html).
+The burden is on you to convince us that it is actually a bug in CoreDNS. This is easiest to do when
+you write clear, concise instructions so we can reproduce the behavior (even if it seems obvious).
+The more detailed and specific you are, the faster we will be able to help you. Check out [How to
+Report Bugs Effectively](http://www.chiark.greenend.org.uk/~sgtatham/bugs.html).
 
-Please be kind. :smile: Remember that CoreDNS comes at no cost to you, and you're
-getting free help.
+Please be kind. :smile: Remember that CoreDNS comes at no cost to you, and you're getting free help.
 
-We are using [Stable Bot](https://github.com/probot/stale) to close inactive issues. If you feel an
-issue should not be closed you can add the "pinned" label to it or just update the bug every now and
-then.
+## Minor Improvements and New Tests
 
-## Minor improvements and new tests
+Submit [pull requests](https://github.com/coredns/coredns/pulls) at any time. Make sure to write
+tests to assert your change is working properly and is thoroughly covered.
 
-Submit [pull requests](https://github.com/coredns/coredns/pulls) at any time. Make
-sure to write tests to assert your change is working properly and is thoroughly
-covered.
+## New Features
 
+First, please [search](https://github.com/coredns/coredns/search?q=&type=Issues&utf8=%E2%9C%93) with
+a variety of keywords to ensure your suggestion/proposal is new.
 
-## Proposals, suggestions, ideas, new features
+If so, you may open either an issue or a pull request for discussion and feedback.
 
-First, please [search](https://github.com/coredns/coredns/search?q=&type=Issues&utf8=%E2%9C%93)
-with a variety of keywords to ensure your suggestion/proposal is new.
+If you are going to spend significant time implementing code for a pull request, best to open an
+issue first and "claim" it and get feedback before you invest a lot of time.
 
-If so, you may open either an issue or a pull request for discussion and
-feedback.
-
-The advantage of issues is that you don't have to spend time actually
-implementing your idea, but you should still describe it thoroughly. The
-advantage of a pull request is that we can immediately see the impact the change
-will have on the project, what the code will look like, and how to improve it.
-The disadvantage of pull requests is that they are unlikely to get accepted
-without significant changes, or it may be rejected entirely. Don't worry, that
-won't happen without an open discussion first.
-
-If you are going to spend significant time implementing code for a pull request,
-best to open an issue first and "claim" it and get feedback before you invest
-a lot of time.
-
-## Vulnerabilities
-
-If you've found a vulnerability that is serious, please email: <team@coredns.io>.
-If it's not a big deal, a pull request will probably be faster.
-
-## Git Hook
-
-We use `golint` and `go vet` as tools to warn use about things (noted golint is obnoxious sometimes,
-but still helpful). Add the following script as a git `post-commit` in `.git/hooks/post-commit` and
-make it executable.
-
-~~~ sh
-#!/bin/bash
-
-# <https://git-scm.com/docs/githooks>:
-# The script takes no parameters and its exit status does not affect the commit in any way.  You can
-# use git # rev-parse HEAD to get the new commit’s SHA1 hash, or you can use git log -l HEAD to get
-# all of its # information.
-
-for d in *; do
-    if [[ "$d" == "vendor" ]]; then
-        continue
-    fi
-    if [[ "$d" == "logo" ]]; then
-        continue
-    fi
-    if [[ ! -d "$d" ]]; then
-        continue
-    fi
-    golint "$d"/...
-done
-~~~
+If possible make a pull request as small as possible, or submit multiple pull request to complete a
+feature. Smaller means: easier to understand and review. This in turn means things can be merged
+faster.
 
 ## Updating Dependencies
 
@@ -98,11 +52,6 @@ Use the following to update the locked versions of all dependencies
 $ make dep-ensure
 ```
 
-To add a dependency to the project, you might run
-```sh
-$ dep ensure github.com/pkg/errors
-```
-
 After the dependencies have been updated or added, you might run the following to
 prune vendored packages:
 ```sh
@@ -111,6 +60,6 @@ $ dep prune
 
 Please refer to Golang's [`dep`](https://github.com/golang/dep) for more details.
 
-# Thank you
+# Thank You
 
 Thanks for your help! CoreDNS would not be what it is today without your contributions.