Add MIT License

[lazyguru]

Not sure how we never had this earlier, but adding it now. @devanbenz please approve to show you are ok with it (or otherwise raise an objection and we can discuss)

[github-actions[bot]]

Go test coverage: 2.7% for commit 6095bdd89d9f17e7c05537bac449d10b82a827d3

View coverage for all packages

```diff # Package Name | Coverage + sublinks/sublinks-federation/internal/lemmy | 2.7% ```

[devanbenz]

LGTM 👍