guideline on process for updating codelists

[wjchulme]

For updating codelists on codelist.opensafely.org. To be added to codelist documentation

[CarolineMorton]

This has been added already but i think we need to add a section on how we convert snomed codelists from the builder into CTV3. I tried to write this before I realised i didn't have a firm grip on it! perhaps @ghickman or @inglesp could add a few words here!

[ghickman]

@inglesp – one for you probably?

[inglesp]

There's some stuff at https://docs.opensafely.org/codelist-creation/ and there's some stuff at https://www.opencodelists.org/docs/ and neither of them reference each other.

I'll work on unifying them.