Docs: Move build instruction and user guide into technical reference

Move build instruction document and user guide document from getting
started into technical references folder. Rename 'tfm_user_guide.rst'
to 'tfm_run_instruction.rst'. This will make the document structure
more clear for readers.

Signed-off-by: Summer Qin <summer.qin@arm.com>
Change-Id: I69d46151f2cb97c828c1b82775ffd1af9032ed45
diff --git a/docs/technical_references/instructions/index.rst b/docs/technical_references/instructions/index.rst
new file mode 100644
index 0000000..19a6e43
--- /dev/null
+++ b/docs/technical_references/instructions/index.rst
@@ -0,0 +1,12 @@
+TF-M Detailed Instructions
+==========================
+
+.. toctree::
+    :maxdepth: 1
+    :glob:
+
+    *
+
+--------------
+
+*Copyright (c) 2021, Arm Limited. All rights reserved.*