Adjust handling of code snippets in `README.rst`
Adjust handling of code snippets in `README.rst`

Declaring the `role:: bash(code)` didn't really do anything, so I
removed it and just used the normal `code` role instead. I also
increased the indentation of these code blocks so they are part of the
list item they belong to. The one instance where a bare `::` was used
instead of `code::` got streamlined and using single backticks without a
link reference was changed to double backticks to signify inline code.

oemof/feedinlib