add docs on how to load a particular config by default

[CarlijnB]

Add documentation on how to on create a (or update the existing) zzz.R file, to load a particular config file by default.

[magicicada]

Low priority, but probably useful

[magicicada]

Suggest: remove ScotEID, but isntead have short section in readme on how to make a default config via zzz.R

@KangarooWasp to add to her previosu readme, will get ported when @CarlijnB ports all that. zzz.R name to be preserved.

[CarlijnB]

@KangarooWasp I'm going to delete the zzz.R file from the Github repo. zzz.R is the conventional name for a script with code that's run upon package loading. In brief, instructions to create a new one are :

Create file zzz.R within the R directory, with code:

.onLoad <- function(libname, pkgname){
  load_config("ScotEID")
}

where "ScotEID" can be replaced with any other pre-installed config file (in /inst/configurations) or alternatively a path to any other config file.

[KangarooWasp]

I've added some documentation to the README.md (and README.Rmd) in the improved-readme branch (7741b9b).

[KangarooWasp]

@CarlijnB do you want to take a look at this to see if you're happy with it?