docs: Documentation restructure

- Change main index structure
- Sort out integration and porting guidelines
- Resort table with releases
- Add Tools section. To be adjusted further for tf-m-tools

Intention to minimise files movement to simplify review process.
Affected files shall be moved later after the new structure agreement.

Signed-off-by: Anton Komlev <anton.komlev@arm.com>
Change-Id: I0352bebabe09d4f7b5e8848ee620c0cea6881c94
diff --git a/docs/integration_guide/platform/index.rst b/docs/integration_guide/platform/index.rst
new file mode 100644
index 0000000..9fd2f2c
--- /dev/null
+++ b/docs/integration_guide/platform/index.rst
@@ -0,0 +1,13 @@
+Porting to a new platform
+=========================
+
+.. toctree::
+    :maxdepth: 1
+
+    porting_TFM_to_a_new_hardware
+    /platform/readme
+    /platform/ext/readme
+
+--------------
+
+*Copyright (c) 2020, Arm Limited. All rights reserved.*