docs: add coding style section

Added to `Getting Started` section, the coding style guidelines.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: I434b63f4816cc7cb5ca91c5cfb8bc24250d152ef
diff --git a/docs/getting_started/index.rst b/docs/getting_started/index.rst
index 090a6e1..733393c 100644
--- a/docs/getting_started/index.rst
+++ b/docs/getting_started/index.rst
@@ -7,6 +7,7 @@
 
    building
    docs-build
+   coding-style
 
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