Add a CONTRIBUTING file.

CONTRIBUTING.md

@@ -0,0 +1,38 @@
+# Contributing to ALE
+
+1. [Guidelines](#guidelines)
+2. [Creating Pull Requests](#pull-requests)
+
+<a name="guidelines"></a>
+
+# 1. Guidelines
+
+Have fun, and work on whatever floats your boat. Take It Easy :tm:.
+
+<a name="pull-requests"></a>
+
+# 2. Creating Pull Requests
+
+For code you write, make sure to credit yourself at the top of files you add, and probably those you modify. You can write
+some comments at the top of your VIM files.
+
+```vim
+" Author: John Smith <john.smith@gmail.com>
+" Description: This file adds support for awesomelinter to the best language ever.
+```
+
+If you want to credit multiple authors, you can comma separate them.
+
+```vim
+" Author: John Smith <john.smith@gmail.com>, Jane Doe <https://jane-doe.info>
+```
+
+# 2.1. Adding a new linter
+
+If you add a new linter, look for existing handlers first in the [handlers.vim](plugin/ale/handlers.vim) file. One of the handlers
+there may already be able to handle your lines of output. If you find that your new linter replicates an existing error handler,
+consider pulling it up into the [handlers.vim](plugin/ale/handlers.vim) file, and use the generic handler in both places.
+
+When you add a linter, make sure the language for the linter and the linter itself are present in the table in the
+[README.md](README.md) file and in the Vim [help file](doc/ale.txt). The programs and linters are sorted alphabetically in the
+table and list.