Improvements to English text

Hi :)

I've spent a bit of time working on polishing some of the English text in GitLab. The quality is pretty admirable for the most part, but I definitely think I've been able to make a worthwhile amount of improvement.

I can reassure you that I haven't lazily cloned the repo, changed the strings, and sent an untested pull request. I took the time to get the dependencies and configuration in place and get `bundle exec rails s` running on `localhost:3000` so that I could test each change properly.

Willing to work on this if there's anything you don't like, so let me know!