Add a dict with common RSS feed file names.

[righettod]

Hi,

This PR propose a dictionary with common file names of RSS feeds:

• The idea was based on this GitHub project.
• Entries were taken from this file.

💡The usage of such dictionary can be in the context of the discovery of hidden content. RSS feed can provide information like for example username format or path convention used (source).

Thank you very much in advance 😃