Docs: Update code structure doc

- fix the number of CPU to 8 to avoid Sphinx crash in OpenCI

Signed-off-by: Anton Komlev <anton.komlev@arm.com>
Change-Id: I4f05857a639ec2609f5b21cb739a6e91e5372fc0
diff --git a/docs/integration_guide/source_structure/index.rst b/docs/integration_guide/source_structure/index.rst
new file mode 100644
index 0000000..426e2a9
--- /dev/null
+++ b/docs/integration_guide/source_structure/index.rst
@@ -0,0 +1,8 @@
+.. toctree::
+    :maxdepth: 1
+
+    source_structure.rst
+
+--------------
+
+*Copyright (c) 2023, Arm Limited. All rights reserved.*