doc: Document Branch Protection

Add Branch Procection related information to the documentation.

Signed-off-by: Gabor Toth <gabor.toth2@arm.com>
Signed-off-by: Gyorgy Szing <gyorgy.szing@arm.com>
Change-Id: Ic67876afc577a28ec6b63ebe85204bb8e3239d30
diff --git a/docs/developer/index.rst b/docs/developer/index.rst
index 3204633..e6ba7ae 100644
--- a/docs/developer/index.rst
+++ b/docs/developer/index.rst
@@ -6,6 +6,7 @@
     :caption: Contents:
 
     arch-overview
+    supported-architectural-features
     project-structure
     service-deployment-model
     service-access-protocols