Upgrade install documentation

[enboig]

I think documentation is a bit outdated, could it be upgraded?

I would install the package with composer require helios-ag/fm-tinymce-bundle; but I had to add config in framework.yaml, maybe a custom file for config would be better (with default vales).

And some examples of use in forms would be interesting.

[helios-ag]

If you can make PR, I will happily merge it