* Update set-up-dropbox.md
Updated text for explanation of DROPBOX_REMOTE_PATH environment variable usage accordingly to how the Dropbox App was scoped during creation.
* Update set-up-dropbox.md
Minor style edit
* Update index.md
Replaced /Apps/my-test-app/some_subdir with /somedir in example value for DROPBOX_REMOTE_PATH environment variable under "Backing up to Dropbox" section, to align with updates done to related "how-to" text