DOC: disambiguate General[ized] Linear Models

The documentation refers to "Generalized Linear Models" for the collection including OLS, ridge regression, etc. This is not "Generalized Linear Models" as usually understood by statisticians - see https://en.wikipedia.org/wiki/Generalized_linear_models - so the use of this term is potentially confusing for people hoping to use GLM in Python.

A better term is "General Linear Models" - see https://en.wikipedia.org/wiki/General_linear_model - so this PR updates the documentation to say that. I hope this is not a controversial suggestion, I merely hope to disambiguate!