Documentation improvements

[seblaeukdd]

I have a few hints about improving the quality of the documentation.

• As I upgraded to latest v2.19.7 , i found that Workflows are there now. However, it is not documented right now.
• In contrast, a 2.20 feature 'Metrics' is already documented.
• Also, some sections like https://semaphoreui.com/docs/user-guide/repositories are not available inside the left hand view, only by editing the URL
• https://semaphoreui.com/install/binary/2_18/config is also not updatet to reflect v 2.19
• The installation section in the docs and on the website are redundant; docs don't point to the config generator
• https://semaphoreui.com/docs/user-guide/apps/ansible#schedule was superseeded by https://semaphoreui.com/docs/user-guide/schedules

Maybe someone can reflect those changes in the documentation?