Doc: document version control policy

Add a page describing how git is used to version control text files.

Change-Id: I607521773ac8e55eae739b81fd9f794eafe74863
Signed-off-by: Gyorgy Szing <Gyorgy.Szing@arm.com>
diff --git a/docs/project/index.rst b/docs/project/index.rst
index d4717d1..83f493f 100644
--- a/docs/project/index.rst
+++ b/docs/project/index.rst
@@ -12,6 +12,7 @@
     license
     maintainers
     versioning_policy
+    version_control
     quality-assurance/index
 
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