Hand_MK5: add coupling law documentation

[Nicogene]

This has been written converting the existing documentation from docx to markdown.

cc @traversaro @ale-git @fiorisi @xEnVrE

[pattacini]

Just a few preliminary comments to begin with:

• We'd need to update https://icub-tech-iit.github.io/documentation/hands.
• We also need to extend the main navigation pane in mkdocs.yml.

[pattacini]

Sorry, I overlooked the point.
Better off dedicating a file for the coupling instead of filling in the main one.
Then, we need to update the main resources pointing to the new file.

[Nicogene]

Sorry, I overlooked the point.
Better off dedicating a file for the coupling instead of filling in the main one.
Then, we need to update the main resources pointing to the new file.

Done

[pattacini]

Nice, thanks!

The page is rendered like this for what concerns the images:

Perhaps, we can increase the resolution so that the variables are more visible?

What do you think @Nicogene?

[pattacini]

I'm merging the PR anyway.
Later, I'll increase the resolution of those images.

[pattacini]

Later, I'll increase the resolution of those images.

Actually, the final rendering is sufficient!