Generate Rmd file for analysis and correct choose results in 06_common.md

[LYU-Daliang]

I want to learn R markdown from the LittleInferenceBook repo, but I find that the md files are helpless in this regard. By modifying the LittleInferenceBook.md, the corresponding Rmd files can be generated, and they are really handy for learning R markdown syntax and format. I'd like to share them with other students.

I am afraid that there is a trivial mistake in 06_common.md: it says choose 0, 1 and n - 1 from n are all 1, but I think choose 0 from n is definitely 1, while choose 1 and n - 1 from n should be n. You can tell it in R: choose(10, 1) and choose(10, 9) are all 10.