[stable2] Add changelog file

[backportbot-nextcloud]

⚠️ This backport had conflicts and is incomplete ⚠️

backport of #1605

[PVince81]

I looked at how we do it in the Talk repo and it seems that on stable branches we only include entries relevant to that branch and older, so I'm going to edit this here accordingly

[PVince81]

ok, so conflict solved: I've synced this branch's README with the one from master and replaced s/master/stable2/

please review!

[PVince81]

some weird stuff here

Error: Unable to process command '::set-env name=TERM::xterm' successfully.
Error: The `set-env` command is disabled. Please upgrade to using Environment Files or opt into unsecure command execution by setting the `ACTIONS_ALLOW_UNSECURE_COMMANDS` environment variable to `true`. For more information see: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/

maybe need to update the CI pipeline config on stable2

[skjnldsv]

maybe need to update the CI pipeline config on stable2

https://github.com/nextcloud/nextcloud-vue/blob/d64d06e568b3c8f248dc1d3447ca0b56ab6c3589/.github/workflows/cypress.yml#L38
Needs to use v2

[PVince81]

maybe need to update the CI pipeline config on stable2

https://github.com/nextcloud/nextcloud-vue/blob/d64d06e568b3c8f248dc1d3447ca0b56ab6c3589/.github/workflows/cypress.yml#L38

Needs to use v2

requested backport: #1548 (comment)