Docs: Add missing platforms to documentation

Add missing documentation for Musca-S1 and AN539

Change-Id: Ic98d3a60c3ea89513a0b5b8cbf6ad6e117506162
Signed-off-by: Marton Berke <marton.berke@arm.com>
diff --git a/docs/user_guides/tfm_integration_guide.rst b/docs/user_guides/tfm_integration_guide.rst
index 7db65a0..c959504 100644
--- a/docs/user_guides/tfm_integration_guide.rst
+++ b/docs/user_guides/tfm_integration_guide.rst
@@ -21,8 +21,10 @@
 
 - Soft Macro Model (SMM) Cortex-M33 SSE-200 subsystem for MPS2+ (AN521)
 - Cortex-M23 IoT Kit subsystem for MPS2+ (AN519)
+- Arm SSE-123 Example Subsystem for MPS2+ (AN539)
 - Musca-A test chip board (Cortex-M33 SSE-200 subsystem)
 - Musca-B1 test chip board (Cortex-M33 SSE-200 subsystem)
+- Musca-S1 test chip board (Cortex-M33 SSE-200 subsystem)
 - CoreLink SSE-200 Subsystem for MPS3 (AN524)
 
 The files related to the supported platforms are contained under the
@@ -40,6 +42,9 @@
 More information about the Musca-B1 test chip board can be found in:
 `Musca-B1 homepage <https://www.arm.com/products/development-tools/development-boards/musca-b1-iot>`__
 
+More information about the Musca-S1 test chip board can be found in:
+`Musca-S1 homepage <https://www.arm.com/company/news/2019/05/arm-demonstrates-new-iot-test-chip-and-board>`__
+
 More information about subsystems supported by the MPS3 board can be found in:
 `MPS3 homepage <https://www.arm.com/products/development-tools/development-boards/mps3>`__