Fixed lock file name and rewording

Reading it, there's a conflict between the "packages file" and the "packages list" files

How about terming `packages.fsx` the "[application] package sources index" and `packages.list`s the "[project] package references list"s ?

Then these get termed the "sources file" and the "references files" ?

I'm not in love with the names them but I also don't like "the packages file" and whatever term is going to be applied to "te packages list" - the terms need to contrast against eachother and yet have meaning independently.

Also, do the terms "application" and "project" make sense in the text (and this comment) ? Or should it be called something more general like "base dir" and "child dirs" ?

Thoughts?