docs: add minimum nodejs version in docs

[inigomarquinez]

The purpose of this PR is to update the documentation to indicate the minimum nodejs version required for each express version, as required here.

I have added this information:

• in the FAQ section
• referenced the FAQ section in the installation guide
• in the express 4.x API
• in the express 5.x API

[!WARNING] Please note that I have only made the change for the English version, as I don't know how translations of content into other languages are handled.