Modify sbt-microsites documentation folder

[AntonioMateoGomez]

This PR modifies the path of the sbt-microsites documentation to be in the default folder for Mdoc.

[calvellido]

docs/docs/docs 🤷‍♂️

[juanpedromoreno]

Could we avoid at least one of the docs subfolders?

[AntonioMateoGomez]

I´m afraid not because Mdoc is going to look into the second level docs folder, so we need an index.md in that level for the landing-home, and we need one more level to set the index.md for the docs layout

[calvellido]

One level is the Scala docs project module. Second one is the mdoc default dir (src/main/tut equivalent). And the third one is where the path to the documentation inside the Jekyll site the docs are being served...

So, unless we change the mdoc directory path, or the project module name, I guess no 🤷‍♂️