Update README.md

[Poussinou]

Hi,

This small PR adds a link to get your plugin on F-Droid 👍

[tareksander]

Thanks, but at the moment the f-droid version doesn't work due to signing issues. I'll add the link to f-droid when these issues are fixed.

[JeffreyO]

Is there any chance of the F-Droid version being fixed soon or should we just stick with the GitHub releases?

[tareksander]

F-droid hasn't responded for a long time, so you still have to use github releases. I'm working on a plugin system for Termux that doesn't require the plugins to be signed with the same key. When that is finished and merged, I can put an update to the f-droid version and it'll work. But that will also take quite a while.