Docs: Add more documentation of TF-M Profiles

Add more information on where the profile documentation can be found.

Change-Id: I1315509a1bfc5e176c5b43a22f6bd426977aa269
Signed-off-by: Raef Coles <raef.coles@arm.com>
diff --git a/docs/getting_started/tfm_build_instruction.rst b/docs/getting_started/tfm_build_instruction.rst
index bfc36ce..a2d4ad4 100644
--- a/docs/getting_started/tfm_build_instruction.rst
+++ b/docs/getting_started/tfm_build_instruction.rst
@@ -162,6 +162,14 @@
 | TFM_CRYPTO_TEST_HKDF        | Test SHA-512 cryptography algorithm | ON            |
 +-----------------------------+-------------------------------------+---------------+
 
+TF-M Profiles
+-------------
+
+TF-M Profiles are implemented as a single cmake configuration file, under the
+``config/profile`` directory. A good understanding can be gained quickly by
+looking at the Profile configuration files, but the ultimate reference for
+Profiles are the design documents in the ``docs/design_documents/profiles/``
+directory.
 
 PSA test configuration
 ----------------------