Update readme for new PAT system of Modrinth

[Andre601]

Modrinth updated their backend which comes with some big changes to their PAT system.

You can now create PATs with fine-grained controls over what permissions it should have (See screenshot below).
The action's readme should mention what scopes are required for it to work (I assume Create versions is one), so that people aren't confused when making a new PAT to use for this Action.

[Kir-Antipov]

The README is already massive, so I would love to reduce its size, not expand it further. I am currently working on creating a standalone documentation for the project where I can provide detailed information on every aspect, including instructions on how to obtain the required tokens.

At the moment, here is the complete list of permissions that mc-publish may require:

• Read projects - this permission is necessary to filter out unsupported loaders for the given project
• Write projects - this permission will be required when I implement Allow specifying the environment of the mod (CurseForge only) #64
• Read versions - this permission is essential for the unfeature functionality to work
• Write versions - this permission is also needed for the unfeature functionality to function correctly
• Create versions - well, this is the whole purpose of mc-publish