Remove duplicate instructions for running locally from `README.md`

We've got lots of duplicate code between README.md and RUNNINGLOCAL.md. Why do we have a RUNNINGLOCAL.md file?

If the answer is [ good reasons ] then we should DRY up the implementation. We shouldn't duplicate this code—that means we'd have to maintain two separate sets of instructions—but instead:

1. delete everything in the README and in the section where we used to explain how to dev locally;
2. provide a link to where the new instructions live; and
3. change the title of the document from RUNNINGLOCAL.md to DEVELOPMENT.md. The official way to run lightning locally is the first section under "Getting Started" and requires docker: https://openfn.github.io/lightning/readme.html#run-via-docker.

What's being described in this new file, it seems, is how to build stuff using Erlang and Elixir from scratch in case you want to do local development. This is the Dev on Lightning Locally section.

Details

We have a separate guide for running lightning locally in RUNNINGLOCAL.md. Some of the instructions are exact duplicates of the instructions in README.md.

We should remove the duplicate instructions from README.md and instead have links that point to the RUNNINGLOCAL.md.

Originally posted by @taylordowns2000 in https://github.com/OpenFn/lightning/pull/2801#pullrequestreview-2545484812

Read README.md and RUNNINGLOCAL.md, comparing the duplicated local-development instructions and the linked "Dev on Lightning Locally" section. Remove the duplicate README.md content, rename RUNNINGLOCAL.md to DEVELOPMENT.md, and update the links so the documentation has one authoritative set of instructions.