Add hlsreport information

[defagos]

Description

This PR adds information about the hlsreport command which, as part of the HTTP Live Streaming Tools, can be used to produce a readable HTML page from the output of mediastreamvalidator.

Changes made

Self-explanatory.

Checklist

• APIs have been properly documented (if relevant).
• The documentation has been updated (if relevant).
• New unit tests have been written (if relevant).
• The demo has been updated (if relevant).