Proposal: Define how Chairs are nominated/replaced

Taken from the governance template
https://github.com/kubernetes/community/blob/master/committee-steering/governance/sig-governance-template-short.md
and modified to define voting for removing a chair.

sig-service-catalog/charter.md

@@ -33,6 +33,15 @@ The following, non-exhaustive, items are out of scope:
     in nature, such as organizing the weekly meetings.
   - A chair does not have more rights, or votes, than a maintainer.
   - Responsible for reporting the SIG’s status to the appropriate Kubernetes leadership teams.
+  - Chairs MAY decide to step down at anytime and MAY propose a replacement, ideally from existing
+    maintainers. Use lazy consensus amongst chairs with fallback on majority vote to accept proposal.
+    This SHOULD be supported by a majority of SIG members.
+  - Chairs MAY select additional chairs through a super-majority vote amongst chairs.
+    This SHOULD be supported by a majority of SIG members.
+  - Chairs MUST remain active in the role and MAY removed from the position
+    if they are unresponsive for > 3 months or are not proactively working
+    with other chairs to fulfill responsibilities. Use lazy consensus amongst chairs with
+    fallback on majority vote.
 
 - Security Contacts
   - MUST be a contact point for the Product Security Team to reach out to for triaging and handling of incoming issues.