CONTRIBUTING: fix formatting of the gist of the guidelines (#1453)
CONTRIBUTING: fix formatting of the gist of the guidelines (#1453)

* CONTRIBUTING: fix formatting of the gist of the guidelines

First level headings for a gist seems to be overkill.

So, replace first level headings with an ordered-list which
sounds more meaningful.

* CONTRIBUTING: specify clearly that 'blame' is a feature of "Git"

The contributing file specifies about the ability to know who wrote
something without the need of @author javadoc tags but incorrectly
attributes the feature to GitHub.

Correctly attribute the feature to where it belongs, Git, and specify
the name of the feature to help users easily take advantage of it.

nicolas-raoul/apps-android-commons,domdomegg/apps-android-commons,nicolas-raoul/apps-android-commons,neslihanturan/apps-android-commons,domdomegg/apps-android-commons,psh/apps-android-commons,domdomegg/apps-android-commons,dbrant/apps-android-commons,neslihanturan/apps-android-commons,misaochan/apps-android-commons,commons-app/apps-android-commons,misaochan/apps-android-commons,neslihanturan/apps-android-commons,maskaravivek/apps-android-commons,misaochan/apps-android-commons,dbrant/apps-android-commons,psh/apps-android-commons,commons-app/apps-android-commons,misaochan/apps-android-commons,nicolas-raoul/apps-android-commons,commons-app/apps-android-commons,domdomegg/apps-android-commons,maskaravivek/apps-android-commons,maskaravivek/apps-android-commons,domdomegg/apps-android-commons,maskaravivek/apps-android-commons,psh/apps-android-commons,maskaravivek/apps-android-commons,misaochan/apps-android-commons,neslihanturan/apps-android-commons,commons-app/apps-android-commons,dbrant/apps-android-commons,neslihanturan/apps-android-commons,psh/apps-android-commons,commons-app/apps-android-commons,psh/apps-android-commons,dbrant/apps-android-commons,misaochan/apps-android-commons,nicolas-raoul/apps-android-commons