Follow up on the affiliation diversity hanlding

This commit adds the note about handling the case
where there are not enough candidates to resolve the
affiliation diversity voilation.

Ref: discussion in
- https://review.opendev.org/c/openstack/governance/+/922512/2/reference/charter.rst

Change-Id: Ib712a6f82d6ed2f6bf7f41c5b088dc6c50c76138

reference/charter.rst

@@ -264,6 +264,11 @@ Technical Committee Member instead of the member whose admission to the
 Technical Committee would cause a violation of the affiliation diversity
 requirement.
 
+If there are not enough candidates to meet the diversity requirement, the
+TC should pass a special resolution to approve alternative solutions, such
+as waiving the diversity requirement, reducing the number of TC seats, or
+holding a special election.
+
 Number of seats to elect
 ========================