Documentation for the CLI

[ernestum]

Right now the CLI is not documented at all while there is lots of documentation for the python API (tutorials, reference).
The documentation for the CLI should include:

• quick start usage examples to paste into the command line
• a table with a mapping between scripts and algorithms
• short descriptions of the non-algorithm scripts with links to them
• a quick intro to Sacred usage for our purposes (ingredients, named configs)
• information about where the output is stored when using the CLI
• list of most important ingredients with links

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• proper documentation of the ingredients in the ingredient packages

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See also #748

Focus on providing a comprehensive set of (working) examples instead of trying to document every piece of the CLI.