Send login instructions by mail after installation (#15)

[fflorent]

Problem

• See #15
  • Missing information about secret key for loging
  • Missing instruction on how to access app if not in public mode

Solution

• Send email with login instructions (secret key included) and instruction on how to access app if not in public mode

PR Status

• [x] Code finished and ready to be reviewed/tested
• [x] The fix/enhancement were manually tested (if applicable)

Automatic tests

Automatic tests can be triggered on https://ci-apps-dev.yunohost.org/ after creating the PR, by commenting "!testme", "!gogogadgetoci" or "By the power of systemd, I invoke The Great App CI to test this Pull Request!". (N.B. : for this to work you need to be a member of the Yunohost-Apps organization)

[fflorent]

!testme

[yunohost-bot]

:carousel_horse:

[fflorent]

!testme

[yunohost-bot]

Alrighty!

[rndmh3ro]

!testme

[yunohost-bot]

Meow :cat2:

[rndmh3ro]

Thanks!