Doc: Added a note on user-guide

This patch adds a command to the build-instructions
in order help guide new users checking out the
dependencies for the first time.

Change-Id: I7409231138de063621a2323cb002a9b67facfb46
Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
diff --git a/docs/user_guides/tfm_build_instruction.rst b/docs/user_guides/tfm_build_instruction.rst
index 774061b..f310bae 100644
--- a/docs/user_guides/tfm_build_instruction.rst
+++ b/docs/user_guides/tfm_build_instruction.rst
@@ -31,6 +31,10 @@
     git clone https://github.com/ARMmbed/mbed-crypto.git -b mbedcrypto-3.0.1
     git clone https://github.com/ARM-software/CMSIS_5.git -b 5.5.0
 
+    # If CMSIS was cloned before the git-lfs dependency was installed,
+    # use the following command to download the binaries.
+    cd CMSIS_5 && git lfs pull
+
 .. Note::
    `CMSIS_5` now uses `git-lfs` for storing large size binaries so the cloning
    process has changed from previous releases. Please refer to the `CMSIS_5`