Update installation docs to fix go command

[bellons91]

I installed Go on my Windows 11 machine.

Then, following the docs, I opened a terminal and run:

go install oss.terrastruct.com/d2

Looks like the command is wrong, as I receive the following message:

go: 'go install' requires a version when current directory is not in a module
Try 'go install oss.terrastruct.com/d2@latest' to install the latest version

I managed to install it using go install oss.terrastruct.com/d2@latest.

Please, update the docs to add the @label part