Fidus Writer documentation corrections

Ubuntu 18.04 https://github.com/fiduswriter/fiduswriter/wiki/Installation-on-Ubuntu-18.04-%28Python-3%29

Note: Say where this file is, and change the wording around the copying of the file.

Configuration

To make any kinds of configurations to how your server is running, copy the file configuration.py-default to configuration.py. Then add any changes to the configuration in the configuration.py file.

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Advanced Configuration on Ubuntu https://github.com/fiduswriter/fiduswriter/wiki/Advanced-Configuration-on-Ubuntu

Note: explain restarting, be explicit

Note: clearly state what is meant by 'virtual environment' and link to the instructions, and below state that all the instruction are to be carried out in the virtual environment.

Note: Fawad says some spelling

Note: this need be clearer about the user, which user is being referred to. As earlier the reader is on the 'Simple instructions' and might have ended with the Fidus Writer 'superadmin' information.

Note: point 4. Sudo user is needed to create this fidus.conf file

4. Create a supervisor configuraton file for fidus writer:

Note: also user could be instructed on how to create and edit these files.