Document creating QRCode with qrencode on CLI

[nakato]

This is important to the use of external OTP auth applications on phones, so add documentation to outline it.

[jleclanche]

PS: When you commit, make sure to use git commit --amend and git push --force to avoid extra commits.

[nakato]

While I would have liked to add this as an option to bna via pure python, adding deps into bna would require a bit of re-factoring of setup.py. The creation of the QR code is extremely important to the use with a phone apps such as FreeOTP, so I think it is worth adding to documentation.

[nakato]

@jleclanche Wouldn't '-' make this an #h2? I was hoping to have this as a #h3 under the OTP section.

[nakato]

Looks like ~'s are more commonly used for H3, I've updated to that. (and they're far less ugly than _'s on title)

[jleclanche]

Thanks!

[nakato]

Cheers