Readme installation instructions give error with flakes (with solution)

[Zaphodious]

Hi there!

When trying to add madness to a config using flakes following the instruction in the readme, I encountered the following error:

error: in pure evaluation mode, 'fetchGit' will not fetch unlocked input 'git+https://github.com/antithesishq/madness.git?exportIgnore=1'

I was able to fix it by adding "rev" to the import statement, pointing at the most recent commit:

"${builtins.fetchGit {
    url = "https://github.com/antithesishq/madness.git";
    rev = "c22c9c03579b7175d94f63e44ee0e518bb5ccdba"
}}/modules"

Thank you for your time!