Add "how to become an aiohttp committer" section (#2498)

* Work on contribution instructions improvement

* Polish text

CONTRIBUTING.rst

@@ -200,6 +200,38 @@ The End
 After finishing all steps make a GitHub_ Pull Request, thanks.
 
 
+How to become an aiohttp committer
+----------------------------------
+
+Contribute!
+
+The easiest way is providing Pull Requests for issues in our bug
+tracker.  But if you have a great idea for the library improvement
+-- please make an issue and Pull Request.
+
+
+
+The rules for committers are simple:
+
+1. No wild commits! Everything should go through PRs.
+2. Take a part in reviews. It's very important part of maintainer's activity.
+3. Pickup issues created by others, especially if they are simple.
+4. Keep test suite comprehensive. In practice it means leveling up
+   coverage. 97% is not bad but we wish to have 100% someday. Well, 99%
+   is good target too.
+5. Don't hesitate to improve our docs. Documentation is very important
+   thing, it's the key for project success. The documentation should
+   not only cover our public API but help newbies to start using the
+   project and shed a light on non-obvious gotchas.
+
+
+
+After positive answer aiohttp committer creates an issue on github
+with the proposal for nomination.  If the proposal will collect only
+positive votes and no strong objection -- you'll be a new member in
+our team.
+
+
 .. _GitHub: https://github.com/aio-libs/aiohttp
 
 .. _ipdb: https://pypi.python.org/pypi/ipdb

docs/spelling_wordlist.txt

@@ -44,6 +44,8 @@ cls
 cmd
 codec
 Codings
+committer
+committers
 config
 Config
 configs