Added license and README

LICENSE

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+MIT License
+
+Copyright (c) 2021 Philipp Wolfer
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# MusicBrainz Auto Tagger Button user script
+
+This is a browser user script to enable the green tagger button ![Open in tagger](https://staticbrainz.org/MB/mblookup-tagger-b8fe559.png)
+on [musicbrainz.org](https://musicbrainz.org), which is used to send a release to [MusicBrainz Picard](https://picard.musicbrainz.org).
+
+It will detect whether Picard is running and will enable the tagger buttons if they are disabled. It
+will even auto detect the proper port on which Picard is listening.
+
+
+## Installation
+
+Install this script with your favorite user script manager (e.g. [Greasemonkey](https://www.greasespot.net/)
+or [Violentmonkey](https://violentmonkey.github.io/)).
+
+The latest version of this script to install is available at:
+
+https://raw.githubusercontent.com/phw/musicbrainz-auto-tagger-button/main/mb-auto-tagger-button.user.js
+
+
+## Gotchas
+
+Some things to be aware off:
+
+- This has been tested only on latest Firefox with Greasemonkey and Violentmonkey. It might or might
+  not work on other browsers. The code assumes your browser supports modern JS features.
+- Actually this hasn’t been tested properly at all. It works here for me, but might not for you. For
+  now this is a proof of concept.
+- For detecting whether and on which port Picard is running this script performs HTTP GET requests
+  on localhost against the ports 8000 - 8020. If you have a local web server or anything else
+  running on one of those ports better make sure it doesn’t do something unexpected. Proper software
+  shouldn’t, but if you have setup a local webserver to delete all your files whenever you open
+  https://localhost:8000 don’t come complain here.
+- If for some obscure reason you have Picard running on a port outside of this port range it won’t
+  work, you’ll have to edit the script for this. Or just configure Picard to run on port 8000 again.
+- Activating the tagger button requires an automatic page reload. The script tries to avoid page
+  reloads unless necessary. Let me know if the reload happens in a situation where it causes issues.
+- Once the tagger button is displayed, it won’t go away even if you close Picard. I found no way to
+  tell MB.org to forget about the `tport` parameter again.
+
+
+## License
+
+MusicBrainz Auto Tagger Button © 2021 Philipp Wolfer <[email protected]>
+
+Published under the MIT license, see LICENSE for details.