Update documentation for Read the Docs

[IsabelParedes]

With this PR, the documentation for Read the Docs is updated. This is intended for version 0.6.0 of jupyros.

Things not included:

• The "References" page still needs to be updated, but this requires modifying the comment blocks in the python package to align with the sphinx format.
• The content "ROS 3D Widgets" page was mostly unmodified (other than formatting), this requires more testing of the widgets to see if they can be used with the updated instructions or if more information needs to be provided.
• There is currently no information about the thread_cell magic
• Playing bag files and live plotting are not documented because some issues were encountered during testing

[hbcarlos]

Thanks, @ihuicatl!