Add how to delete a media and its file from Fedora

[rosiel]

GitHub Issue: #1208

What does this Pull Request do?

Updates ONLY the section of the Media documentation dealing with "replacing" files or media.

What's new?

• reworded to be more explanatory
• somewhat reworded to remove assumption of using Fedora
• Need to continue to reword the rest of this document, but that would take more time than I have now, and this could be seen as an incremental improvement.
• No new dependencies.
• This is kind of a bug that we are documenting (or a lack of a feature), so while it addresses Document how to replace a media #1208 it does not resolve @mjordan 's suggestion of adding the feature 'as we expect it to work'.

How should this be tested?

Please read docs. Does make sense? Few/no typos? Formatting !!!note will not show up in Github, but will at github.io.

Additional Notes:

Interested parties

Tag @mjordan @manez

[manez]

Improved explanation and warnings!

[mjordan]

Agreed, merging.

[kayakr]

@rosiel typo s/exising/existing