rendering profiles should show a short description

Submitted by antistress @anti-stress

Link to original bug (#7436)

Description

Hi,

When it's time to render a project into an A/V file, user has the ability to select a preset (even if at present time Pitivi shows only one preset!).
These preset names should be followed by a short description to help the user to pick one.

I would suggest a 2 lines description :
The 1st line would aim at being objective/descriptive/informative
The 2nd line would be more subjective, in the form of an advice

For an exemple, see the last part of #1809 (closed) about creating a preset named "archiving (lossless)" which could lead to a description like :

• 1st line : "for video archiving, using lossless audio and video codecs, standardization by IETF pending" (and later : "for video archiving : using lossless audio and video codecs, standardized by IETF")
• 2nd line : "no compomise : the best possible quality at the expense of file size"

Thanks