Replace submission URL copy with something that suggests Google Sheets intergration

[yanokwa]

Currently under Submission URL, it says...

Directs your submissions somewhere other than the Aggregate that supplied the form. This is the ODK Aggregate website url with Aggregate.html replaced by submission.

It would be nicer to replace it with...

Directs your submissions somewhere other than the server that supplied the form. This is often used to submit data directly to Google Sheets.

This is blocking on https://github.com/opendatakit/docs/issues/748