docs(prerequisites): update mbedtls version used

With Commit@55aed7d798f3d48d6aa08d58eb46c4cda318bcfb
we have now updated to use mbedtls 3.6.0.

Update document to reflect the same.

Change-Id: I6bd8fcca795373a05bc6beb2e085d24fdd14932f
Signed-off-by: Govindraj Raja <govindraj.raja@arm.com>
(cherry picked from commit d963c6badeecea264ad49e998a111946a1b33ce6)
diff --git a/docs/getting_started/prerequisites.rst b/docs/getting_started/prerequisites.rst
index 5a4e503..0469b1b 100644
--- a/docs/getting_started/prerequisites.rst
+++ b/docs/getting_started/prerequisites.rst
@@ -77,7 +77,7 @@
 The following libraries are required for Trusted Board Boot and Measured Boot
 support:
 
-- mbed TLS == 3.4.1 (tag: ``mbedtls-3.4.1``)
+- mbed TLS == 3.6.0 (tag: ``mbedtls-3.6.0``)
 
 These tools are optional: