Add README.md for gi

plugins/gi/README.md

+gitignore (gi) plugin
+=====================
+
+This plugin provides a simple command line interface to gitignore.io - a
+website that generates .gitignore files based on your project requirements.
+
+## Completions
+
+The first step is to download the latest language list from gitignore.io so
+that the fish completions can be updated.  Run `gi update-completions` to
+download the completions, they will be stored in
+`~/.config/fish/completions/gi.fish`
+
+You should repeat this occasionally to keep up to date.
+
+## Usage
+
+Type `gi` followed by TAB to view the list of languages available.  To generate
+a .gitignore file, specify the list of languages you are interested in and pipe
+the output into the destination file.  Example for a go-lang project:
+
+    gi go tags vagrant > .gitignore
+    git add .gitignore