fix + docs: Correct some grammar on `About` page and document local dev

Hey there! I hope this isn't too bikeshed-ish, but I corrected some grammar mistakes and antiquated language on the About page. I also documented how to build the project locally. I was having trouble with Docker/devcontainers on my internet, so I hope it helps folks get started faster than me! ☺️

However, I didn't complete everything I wanted to finish: some strings wouldn't change, even with a lot of makemessages and compilemessages commands. I'll leave my 'draft' for these below. If someone more experienced with Django i8n comes along, they might be able to use them!

before	after
To control GNOME Shell extensions using this site you must install GNOME Shell integration that consists of two parts: browser extension and native host messaging application	To control GNOME Shell extensions using this site, you must install GNOME Shell integration, which consists of a browser extension and a native host messaging application
Click here to install browser extension	Click here to install the browser extension
See %swiki page%s for native host connector installation instructions	To install the native host connector, see %sits wiki page%s for instructions

If anyone knows why these changes don't work, please let me know, and I'll take care of these myself. Thank you! 😌️