templates: nomination: Clarify its purpose

This commit updates the "Contributor Nomination" template to make its
purpose clear and straight forward -- that this template is for
requesting the Triage permission level.

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: stephanosio

.github/ISSUE_TEMPLATE/nomination.md

@@ -17,8 +17,9 @@ with the lowest [GitHub Permission Level] of Read. For example, Contributors
 with Read permission do not have the permission to add reviewers to a pull
 request.
 
-Use this template to nominate a GitHub user for an elevated permission level in
-the Contributor role.
+Use this template to nominate a GitHub user for the Contributor role with
+Triage permission level, which allows the user to add reviewers to a pull
+request and be added as a reviewer by other users.
 
 # Nomination