Update param description to make it more user-friendly

Update some outdate parameter descriptions to make it more clear to
users on how to set the params.

Signed-off-by: Xinyu Zhang <xinyu.zhang@arm.com>
Change-Id: I3cc83ec51a30b51c0b2eb04fc4725f243b698ad8
diff --git a/tf-m-static-checks.yaml b/tf-m-static-checks.yaml
index d169da8..af7151d 100644
--- a/tf-m-static-checks.yaml
+++ b/tf-m-static-checks.yaml
@@ -20,25 +20,28 @@
       - string:
           name: 'GERRIT_HOST'
           description: |
-            For use when triggering with unmerged Gerrit changes.
+            No need to change.
       - string:
           name: 'GERRIT_REFSPEC'
           default: '+refs/heads/*:refs/remotes/origin/*'
           description: |
-            For use when triggering with unmerged Gerrit changes.
+            Specify which TF-M version to use
+            refs/heads/<branch_name> : Pick up latest HEAD on branch
+            TAG_NAME                 : Pick up a tagged version
+            full commit hash         : Pick up a specific commit.
       - string:
           name: 'GERRIT_BRANCH'
           default: 'master'
           description: |
-            For use when triggering with unmerged Gerrit changes.
+            TF-M branch.
       - string:
           name: 'GERRIT_CHANGE_NUMBER'
           description: |
-            For use when triggering with unmerged Gerrit changes.
+            No need to change.
       - string:
           name: 'GERRIT_PATCHSET_REVISION'
           description: |
-            For use when triggering with unmerged Gerrit changes.
+            No need to change.
       - string:
           name: 'CODE_REPO'
           default: 'https://review.trustedfirmware.org/TF-M/trusted-firmware-m'