docs(memory-management): Add documentation on S1 memory management

This patch also adds the Coverity Scan badge to the RMM Readme.rst

Signed-off-by: Javier Almansa Sobrino <javier.almansasobrino@arm.com>
Change-Id: I12de320a57ea64844b77d22d9c9fd9270bf9415c
diff --git a/docs/design/index.rst b/docs/design/index.rst
index 264c841..f1d6059 100644
--- a/docs/design/index.rst
+++ b/docs/design/index.rst
@@ -9,6 +9,7 @@
     :numbered:
 
     locking
+    memory-management
     file-org-and-config
     fake-host-architecture
     cold-and-warm-boot-design