group examples should be documented

[luisan00]

Description

examples/doc.txt should be documented, the file actually contains few lines:

/**
 * @defgroup examples Mesh4all Examples
 * ## This is example-doc
 * All about the Mesh4all examples.
 */

But it should shown us:

• Description; What is it? or; what it's not
• Purpose of an example and refs or links (using doxygen syntax ) to current and functional examples
• Useful information xD

I think boards/doc.txt is a good example of what it should be.

Useful links

https://github.com/Mesh4all/m4a-firmware/blob/main/boards/doc.txt

[luisan00]

it's ready @eduazocar ?