List major changes in LTS initial release

From https://github.com/nodejs/node/pull/41305#discussion_r775147261:

Document it. Make sure it gets highlighted in the changelog for 18.x

That comment tweaked a peeve of mine. When a release line is promoted to "Current", it gets a nice post like https://medium.com/the-node-js-collection/node-js-16-available-now-7f5099a97e70 or https://nodejs.org/en/blog/release/v8.0.0/ to list all of the major changes in that release. This is great... for people following the "Current" line.

I am sure there are many people, such as myself, who only follow the LTS line. When that "Current" release toggles over to LTS, we see posts like https://nodejs.org/en/blog/release/v16.13.0/. This does not give nearly as much detail about the things LTS users should consider during their update, i.e. no detail at all. It would be very helpful if the LTS release notes included a summary of the major changes in the overall release, or at least a link to the initial summation post. (This might be a reiteration of https://github.com/nodejs/Release/issues/635#issuecomment-748372512.)

I'm not sure what the process is, or how it would need to change, in order to make this a reality. Making a wild guess, it could be that adding a label to things that should be called out and then referencing that label when generating the new LTS release would suffice.

Start with the linked Node.js pull request discussion and Release issue #635, then compare the referenced Current and LTS release posts. Determine how major changes are identified and carried into LTS notes; done means documenting an agreed process or output that gives LTS users a summary or link to the initial release overview.