doc updates (#1563)

Capatilize coredns in ADAPTERS.md

ADOPTERS.md

@@ -3,6 +3,6 @@
 * [Kismia](https://kismia.com) uses CoreDNS for Kubernetes cluster DNS.
 * [Admiral](https://getadmiral.com) uses CoreDNS to handle geographic DNS requests for our public-facing microservices.
 * [Qunar](https://qunar.com) uses CoreDNS for service discovery of its GPU machine learning cloud with TensorFlow and Kubernetes.
-* [seansean2](https://web.mit.edu) uses coreDNS in production at MIT for DNS.
+* [seansean2](https://web.mit.edu) uses CoreDNS in production at MIT for DNS.
 * [Tradeshift](https://tradeshift.com/) uses CoreDNS to look up company identifiers across multiple shards/regions/zones
 * [SoundCloud](https://soundcloud.com/) uses CoreDNS as internal cache+proxy in Kubernetes clusters to handle hundreds of thousands DNS service discovery requests per second.

plugin.md

@@ -8,9 +8,9 @@ The main method that gets called is `ServeDNS`. It has three parameters:
 * `dns.ResponseWriter` that is, basically, the client's connection;
 * `*dns.Msg` the request from the client.
 
-`ServeDNS` returns two values, a response code and an error. If the error is not nil CoreDNS
-will return a generic SERVFAIL to the client. The response code tells CoreDNS if a reply has been
-written by the plugin chain or not. In the latter case CoreDNS will take care of that.
+`ServeDNS` returns two values, a response code and an error. If the error is not nil CoreDNS,
+will return a SERVFAIL to the client. The response code tells CoreDNS if a *reply has been
+written by the plugin chain or not*. In the latter case CoreDNS will take care of that.
 
 CoreDNS treats:
 
@@ -23,7 +23,8 @@ as special and will then assume *nothing* has been written to the client. In all
 assumes something has been written to the client (by the plugin).
 
 The [*example*](https://github.com/coredns/example) plugin shows a bare-bones implementation that
-can be used as a starting point for your plugin.
+can be used as a starting point for your plugin. This plugin has tests and extensive comments in the
+code.
 
 ## Hooking It Up