Ignite-1209 and "How to contribute" page has been updated

[Artem Shutak]

Igniters,

I've been created and fixed
https://issues.apache.org/jira/browse/IGNITE-1209 (Improve
git-format-patch.sh to add rev. number to patch-file name).

Also, I've added to
https://cwiki.apache.org/confluence/display/IGNITE/How+to+Contribute wiki
page section "For commiters", which contains useful information according
to ignite-1209 and etc.

Please, review wiki.

-- Artem --