Explain why support_test_psa_compliance is needed

Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index d86a9f7..449b213 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -2765,6 +2765,7 @@
 }
 
 support_test_psa_compliance () {
+    # psa-compliance-tests only supports CMake >= 3.10.0
     ver="$(cmake --version)"
     ver="${ver#cmake version }"
     ver_major="${ver%%.*}"