This commit extends the developer docs for `lldb-dap`. It also adds a
short "Contributing" section to the user-facing README.
Last but not least, it updates the `repository` in the package.json to
point to the actual source of truth for the source code, instead of
pointing to its mirrored repository. I hope that the VS Code Marketplace
properly supports the `directory` property. Unfortunately, I have no way
to test this before merging this Pull Request.
6c137b75f3