The Windows (WSL) installation guide is out-of-date

I was trying to install frama-c on WSL by the guide on the website, and got stuck with the opam install -y depext command with the following error:

[ERROR] depext unmet availability conditions, e.g. 'opam-version >= "2.0.0~beta5" & opam-version < "2.1"'

It took me a while to figure out that in fact opam-depext has been integrated into opam since 2.1 and it is sufficient to just run opam install frama-c as described in the Linux installation guide.

Therefore I suggest that the WSL installation guides on the frama-c webpage and repository be updated to prevent others, who are using WSL, to be confused.