docs(tags) add docs explaining plans for tags. update readme.

Chat a bit about how tags are planned to work, update readme to remove information
which is no-longer true, as well as to point to the tags docs.
feat(index) add file watch as primary way to tell if changes made

stop waiting for close of evim, begin watching for change to file. Prevent the issue
of having to close the whole evim program. Add comments to tagging file, improve
handling of errors and blank strings