Sync only a section of a file.

I would like to sync only a section of one file to another file. In my readme.txt file I have the Changelog secion.
I want to sync only the text below the Chnagelog Heading and before the Ugrade Notice Heading

== Changelog ==
ONLY THIDS SHOULD BE SYNCED TO ANOTHER FILE, IT MAY EVEN BE IN THE SAME REPOSITORY , IE /chnagelog/changelog.md
== Upgrade Notice ==

Thank you