[gazelle] update gazelle readme to make tables readable

[tjoneslo]

The table syntax for the Github markdown is much more limited than the table syntax for the generated docs. So fix the Gazelle Readme so the docs appear as readable.

Add the sourceset root, strip resources prefix and include binary directives. in the documentation.

[stevebarrau]

Could we use .rst and have tables that look like this? Note how this spans both columns.

[tjoneslo]

Could we use .rst and have tables that look like this? Note how this spans both columns.

Conversion to RST requires a whole lot more formatting changes. I understand the idea, but it's not a very simple change