Documentation request for X² test

[bvenn]

Description

A proper explanation/tutorial for handling chi-squared-tests is missing. There seems to be at least three versions of the Chi-Square test existing:

• distribution test
• independence test
• homogenity test

A description is needed that introduces the core concept of the X²-distributed test statistic and how to apply the tests.

@omaus started to look at the test in #181 but I think there is some sort of proper description missing for which test requires which parameters etc.

Thanks for pointing this out @matthewcrews :rocket: