Update Statistics.md

[vuhlmann]

Modified content to address most comments and fixed a few typos

[vuhlmann]

The reference list (references.bib) must be updated to include the following:

@ARTICLE{Lever2017-pca, title = "Principal component analysis", author = "Lever, Jake and Krzywinski, Martin and Altman, Naomi", journal = "Nat. Methods", volume = 14, pages = "641--642", month = july, year = 2017, language = "en" }

[bethac07]

Thanks Virginie! Do you want to add that reference to the citation file, or would you like me to?

[vuhlmann]

I tried to edit this file myself but miserably failed for some reason. Let me try again!

[vuhlmann]

Done!