Docs: Add topic for interface changes

As there is no proper topic for interface changes now.

Signed-off-by: Ken Liu <Ken.Liu@arm.com>
Change-Id: Ia9f27b954f24e9da6a0c8d94f6e1ac888784148f
diff --git a/docs/contributing/code_review_guide.rst b/docs/contributing/code_review_guide.rst
index 0677b29..5b260c2 100644
--- a/docs/contributing/code_review_guide.rst
+++ b/docs/contributing/code_review_guide.rst
@@ -211,6 +211,7 @@
 Docs           All \*.rst changes.
 Dualcpu        Dual-cpu related changes.
 HAL            Generic HAL interface/implementation changes.
+Interface      Interface changes, either Non-source and secure.
 Pack           For packing purpose.
 Platform       Generic platform related changes under `platform/*`.
 Platform Name  Specific platform changes.