Update README.md for DevTools plugin

[jeanlouisferey]

Hey, I just made a Pull Request!

I did a little correction in the README.md for DevTools plugin. To configure the package dependencies, you have to add in app-config.yaml the list of packages prefixes you want to be listed (by default only @backstage and @internal are listed).

If you follow the doc, you will have a problem when you start Backstage with yarn dev:

[0] 
[0] YAMLParseError: Plain value cannot start with reserved character @ at line 89, column 9:
[0] 
[0]       - @immobiliarelabs/backstage-
[0]         ^
[0] 
[0] 
error Command failed with exit code 1.

You have to add single quotes around packages prefixes.

I updated the doc for that.

:heavy_check_mark: Checklist

• [X] A changeset describing the change and affected packages. (more info)
• [X] Added or updated documentation
• [ ] Tests for new functionality and regression tests for bug fixes
• [ ] Screenshots attached (for UI changes)
• [X] All your commits have a Signed-off-by line in the message. (more info)

[backstage-goalie[bot]]

Missing Changesets

The following package(s) are changed by this PR but do not have a changeset:

• @backstage/plugin-devtools

See CONTRIBUTING.md for more information about how to add changesets.

Changed Packages

Package Name	Package Path	Changeset Bump	Current Version
@backstage/plugin-devtools	plugins/devtools	none	v0.1.9-next.2

[github-actions[bot]]

Uffizzi Cluster pr-22854 was deleted.

[freben]

I rudely added a comment to that effect to get the change in for the release! Hope that's OK.

[awanlin]

Thanks again for this contribution @jeanlouisferey! 🚀

Thanks for the reviews and merge @freben @vinzscam 👍