Create detailed walkthrough for mentors

[ZooeyMiller]

I may have just not found it somewhere in the file, but for we teach FAC11 we want to have detailed notes for what we need to run through in the code along.

Don't want to leave anything important out.

[ZooeyMiller]

This is almost done (in 09e679a) the last bit that is still needed is step 5 to be updated to finish off showing everyone how to modularise the code.

As said in the commit message:
"my plan is for this not to be merged into master but left in a branch for the mentors to us for the code-along, but that the repo as it stands is kept clean"