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>
diff --git a/docs/getting_started/prerequisites.rst b/docs/getting_started/prerequisites.rst
index 0d4331f..6a0241f 100644
--- a/docs/getting_started/prerequisites.rst
+++ b/docs/getting_started/prerequisites.rst
@@ -31,7 +31,7 @@
 Clang/LLVM               11.0.0
 Device Tree Compiler     1.4.7
 GNU make                 3.81
-mbed TLS\ [#f1]_         3.4.1
+mbed TLS\ [#f1]_         3.6.0
 Node.js [#f2]_           16
 OpenSSL                  1.0.0
 Poetry [#f2]_            1.3.2