added a new document about how we are using Git

contributing/code/git.rst

@@ -0,0 +1,42 @@
+Git
+===
+
+This document explains some conventions and specificities in the way we manage
+the Symfony code with Git.
+
+Pull Requests
+-------------
+
+Whenever a pull request is merged, all the information contained in the pull
+request (including comments) are saved in the repository.
+
+You can easily spot pull request merges as the commit message always follows
+this pattern:
+
+.. block: text
+
+    merged branch USER_NAME/BRANCH_NAME (PR #1111)
+
+The PR reference allows you to have a look at the original pull request on
+Github: https://github.com/symfony/symfony/pull/1111. But all the information
+you can get on Github are also available from the repository itself.
+
+The merge commit message contains the original message from the author of the
+changes. Often, this can help understand what the changes were about and the
+reasoning behind the changes.
+
+Moreover, the full discussion that might have occurred back then is also
+stored as a Git note (before March 22 2013, the discussion was part of the
+main merge commit message). To get access to these notes, add this line to
+your ``.git/config`` file:
+
+.. block: text
+
+    fetch = +refs/notes/*:refs/notes/*
+
+After a fetch, getting the Github discussion for a commit is then a matter of
+adding ``--show-notes=github-comments`` to the ``git show`` command:
+
+.. block: text
+
+    git show HEAD --show-notes=github-comments

contributing/code/index.rst

@@ -10,4 +10,5 @@ Contributing Code
     tests
     standards
     conventions
+    git
     license