Docs: A bunch of small fixes

- remove "Migration from legacy buildsystem" as obsolete
- update the list of topics in Contribution guide
- update broken links in the Glossary
- add a link to TF-M forum in introduction
- update "Code Sharing" guide
- change warning of usage the default keys
- update mbedTLS repository URL

Signed-off-by: Anton Komlev <anton.komlev@arm.com>
Change-Id: I8a2fa1802fddfa0a098f3999c0fffb5d0d003d06
diff --git a/docs/glossary.rst b/docs/glossary.rst
index 83e283d..f80c614 100644
--- a/docs/glossary.rst
+++ b/docs/glossary.rst
@@ -90,9 +90,8 @@
         for ARMv8-M.
 
     TBSA-M
-        Trusted Base System Architecture for Armv6-M, Armv7-M and Armv8-M.
-        TBSA term. See `Trusted Base System Architecture for Armv6-M, Armv7-M
-        and Armv8-M`_
+        Trusted Base System Architecture for M.
+        TBSA term. See `Trusted Base System Architecture for M`_
 
     MPC
         Memory Protection Controller:
@@ -127,16 +126,18 @@
 
 .. rubric:: Reference
 
-| `PSA Firmware_Framework for M`_
+| `Firmware Framework for M (FF-M)`_
 
-.. _PSA Firmware_Framework for M: https://pages.arm.com/psa-resources-ff.html
+.. _Firmware Framework for M (FF-M):
+   https://www.arm.com/architecture/security-features/platform-security
 
-.. _PSA term: `PSA Firmware_Framework for M`_
+.. _PSA term: `Firmware Framework for M (FF-M)`_
 
-| `Trusted Base System Architecture for Armv6-M, Armv7-M and Armv8-M`_
+| `Trusted Base System Architecture for M`_
 
-.. _Trusted Base System Architecture for Armv6-M, Armv7-M and Armv8-M: https://pages.arm.com/psa-resources-tbsa-m.html
+.. _Trusted Base System Architecture for M:
+   https://www.arm.com/architecture/security-features/platform-security
 
 --------------
 
-*Copyright (c) 2017-2020, Arm Limited. All rights reserved.*
+*Copyright (c) 2017-2022, Arm Limited. All rights reserved.*