Added more config file options, updated readme

I added more troubleshooting to the readme and more config file options
for TOTP issuer name, enabling/disabling image embeds (and their
maximum width), and HTML you can easily append to the footer.
Also, added some items to the gitignore so production servers won't show
tons of changes in git status.
Status Job ID Name Coverage
  Test
canceled #215976291
rspec-integration