Add warning about required actions permissions on README.md

[marcalexiei]

Greetings,
Today I setup changeset action for the first time in one of my repository.
During the process I encountered various errors regarding permissions.

This PR adds a warning before all example workflows mentioning the 2 main methods to provide the action a GITHUB_TOKEN with the correct permissions.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 27d143e

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

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[GauBen]

Ran into this very problem today, it would have been very helpful to have this directly in the readme

Thanks for the documentation @marcalexiei

[toomuchdesign]

Just an extra note to specify that the full needed permissions seem to be:

contents: write
pull-requests: write
actions: write

actions seems to be needed in order for the dependency update PR tu run the relevant CI actions. Otherwise CI actions will be created and stay stale.

[MrLightful]

Also, having a repo in organization, I had to Allow GitHub Actions to create and approve pull requests (Settings->Actions->General).
But before I could so on repo level, you need to do it on org level first.

There is no appropriate keyword for this in permissions, it needs to be done via UI, right?