Merge pull request #22 from QiufangMa/main

AD review comments from Mahesh

Update draft-ietf-netmod-immutable-flag.md

update date

fix nits

Merge pull request #15 from QiufangMa/main

fix nits && yang formating

Merge pull request #14 from QiufangMa/main

follow-up comments from Rob and Kent

Merge pull request #13 from QiufangMa/main

Fix some nits, eliminate redundant statement, etc

Update ietf-immutable-annotation.yang

fix nits

fix city info