Docs: Refine tfm_sw_requirement.rst

Simplify the tfm software requirement document and change the document
to 'tfm_getting_started.rst', let it more
suitable for new starter.

Signed-off-by: Summer Qin <summer.qin@arm.com>
Change-Id: I10379aa92ac2c6cd784f0fd1b1b5431243716d74
diff --git a/docs/technical_references/instructions/tfm_build_instruction.rst b/docs/technical_references/instructions/tfm_build_instruction.rst
index 116b5d1..49bdeff 100644
--- a/docs/technical_references/instructions/tfm_build_instruction.rst
+++ b/docs/technical_references/instructions/tfm_build_instruction.rst
@@ -2,7 +2,7 @@
 Build instructions
 ##################
 Please make sure you have all required software installed as explained in the
-:doc:`software requirements </docs/getting_started/tfm_sw_requirement>`.
+:doc:`TF-M getting started </docs/getting_started/tfm_getting_started>`.
 
 ****************
 TF-M build steps
@@ -31,7 +31,7 @@
 .. Note::
 
  - For building with Armclang compiler version 6.10.0+, please follow the note
-   in :doc:`software requirements </docs/getting_started/tfm_sw_requirement>`.
+   in :doc:`TF-M getting started </docs/getting_started/tfm_getting_started>`.
  - For building with the IAR toolchain, please see the notes in
    :doc:`IAR software requirements <tfm_build_instruction_iar>`