Update contributing statement

CONTRIBUTING.md

@@ -7,12 +7,19 @@ Please make sure that all packages you commit or request to pull:
 * Have no dependencies outside the openwrt core packages or this feed.
 * Are "run tested" (or at least compile tested)
 
-Please make sure that every commits you make to this repository:
+Please make sure that all commits you make to this repository:
 * Are signed-off (see https://dev.openwrt.org/wiki/SubmittingPatches#a10.Signyourwork)
 * Have a proper description (starting with <package-name>: / including <package-name>)
 
 If you have commit access:
-* Never ever git push --force on master!!!
-* Do not touch other maintainer's stuff if you're not sure
-* You can still use Pull Request to ask for comments
+* Do NOT use git push --force.
+* Do NOT commit to other maintainer's packages without their consent.
+* Use Pull Requests if you are unsure and to suggest changes to other maintainers.
 
+Release Branches:
+* Branches named "for-XX.YY" (e.g. for-14.07) are release branches.
+* These branches are built with the respective OpenWrt release and are created
+  during the release stabilisation phase.
+* Please ONLY cherry-pick or commit security and bug-fixes to these branches.
+* Do NOT add new packages and do NOT do major upgrades of packages here.
+* If you are unsure if your change is suitable, please use a pull request.