~cedric/newspipe-docs

new: added an example on how to look for an article via the API.
Removed section about deployment with docker and updated section about migrations.
Updated documentation with commands from the built-in Flask cli.
fixed wrong level of titles
Moved section related to the updates and migrations.
reformated introduction and added section about deployment with docker.
added link to GitHub sponsor.
fixed title level
example of cron rule
Updated cdeplyment section with the new name of the provided configuration file in Newspipe.
added link to the documentation of the API.
moved some sections in the README.