Update README.md

[gchenuet]

Hey!

Thanks a lot for your plugin, super useful!

A quick PR to improve the README:

• Fix package path
• Add information about Slack scopes

[zhammer]

thanks @gchenuet !

[github-actions[bot]]

:tada: This PR is included in version 1.0.0 :tada:

The release is available on @seatgeek/backstage-plugin-gitlab-catalog-backend@1.0.0

Your semantic-release bot :package::rocket:

[github-actions[bot]]

:tada: This PR is included in version 1.0.2 :tada:

The release is available on @seatgeek/backstage-plugin-slack-catalog-backend@1.0.2

Your semantic-release bot :package::rocket: