[chore] Add Feditext as recommended client

[daenney]

Description

With Feditext now accepting beta users, this adds it as the third client to recommend so we have web and the dominant mobile platforms covered.

This also removes the screenshots from the README, because it became a mess trying to add a third one. Either the cells become very narrow, or the table doubles in height. As the UI may also change over time, it might be better to point folks at the apps instead who'll hopefully have up to date screenshots in their storefronts.

Checklist

Please put an x inside each checkbox to indicate that you've read and followed it: [ ] -> [x]

If this is a documentation change, only the first checkbox must be filled (you can delete the others if you want).

• I/we have read the GoToSocial contribution guidelines.
• I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
• I/we have performed a self-review of added code.
• I/we have written code that is legible and maintainable by others.
• I/we have commented the added code, particularly in hard-to-understand areas.
• I/we have made any necessary changes to documentation.
• I/we have added tests that cover new code.
• I/we have run tests and they pass locally with the changes.
• I/we have run go fmt ./... and golangci-lint run.

[tsmethurst]

Nice one :)