text: Title: Incorrect Description of Changing cell type
  Body: [Changing Cell's Type](https://euporie.readthedocs.io/en/latest/apps/notebook.html#changing-a-cell-s-type) has incorrect description .
  It is explaining `how to close notebook` instead of `how to change cell's type`.
  Corresponding [file](https://github.com/joouha/euporie/blob/main/docs/apps/notebook.rst#changing-a-cells-type) in repo. 
  Maybe we can add good first issue