Documentation for the recent mimetype files

[rullzer]

PR for #1307

Not to much text. But then again how much is really needed?

CC: @MorrisJobke @PVince81 @Xenopathic

[MorrisJobke]

s/trough/through/

[rullzer]

fixed

[MorrisJobke]

Fine with me.

cc @carlaschroder Please have a look at the location. :)

[RobinMcCorkell]

We could do with a short list and description of common mimetype aliases in the relevant file, for example:

• image
• image/vector
• audio
• font
• x-office/document
• x-office/spreadsheet
• x-office/presentation
• text/code

Those are likely to be the most common ones that an administrator would want to add. And a note that states that to convert to an icon, the first part of the mimetype (the bit before the /) will be checked if the full mimetype cannot be found, so audio/foobar will still get an audio icon.

[carlaschroder]

This is good, @rullzer, thank you. I agree with Xenopathic; some examples and a little more explanation is very helpful.
@MorrisJobke I'm going to do a bit of re-organizing, so this is fine where it is for now.

[carlaschroder]

I'll go ahead and merge this; it can always be expanded later. (meaningful look at @Xenopathic)

[RobinMcCorkell]

As a wise man once said, "Ask and thou shalt receive": #1373 😄