Improve CONTRIBUTING.md

Signed-off-by: Etienne CHAMPETIER <champetier.etienne@gmail.com>

CONTRIBUTING.md

@@ -5,7 +5,14 @@ Please make sure that all packages you commit or request to pull:
 * Have yourself or another person listed in the (PKG_)MAINTAINER field.
 * Will be updated regularly to maintained and supported versions.
 * Have no dependencies outside the openwrt core packages or this feed.
+* Are "run tested" (or at least compile tested)
 
-Please sign-off all your commits / pull requests to this repository. See:
-https://dev.openwrt.org/wiki/SubmittingPatches#a10.Signyourwork
+Please make sure that every 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