Add instructions for installation from the zip

[Kommynct]

It's just a bunch of files i have no idea what to do with, if there was just a quick wiki explanation i'd super appreciate it, thank you

edit: figured it out for chrome, go to chrome://extensions, click developer options, click pack extension, choose the root directory, install it by dragging it onto chrome://extensions

[Trophonix]

I submitted a pull request: https://github.com/KoffeinFlummi/alientube/pull/8

[ImmortalFishy]

I switched from Chrome to Firefox recently. While the release version installed easily offline as well as having a copy of it on the Chrome web store, I don't know exactly how to compile the add-on as an XPI. I tried manually adding it to get signed and used locally but had some errors. Could use some help figuring out how to properly install it, or just have someone knowledgeable upload it to the Firefox addon website, because the only other reddit/youtube addon on there doesnt seem to work, so it could be useful to have for people who aren't aware of the Github page.

[TP18]

@KoffeinFlummi how do I install it on Safari? Where do I have to do the instructions given? Terminal? where put the folder?