Bug 1170608: Update data collection documentation.
Bug 1170608: Update data collection documentation.

Includes the proposed change to trigger metrics events for all link clicks
instead of just about:accounts link clicks.

mozilla/snippets-service,glogiotatidis/snippets-service,Osmose/snippets-service,Osmose/snippets-service,mozmar/snippets-service,mozmar/snippets-service,glogiotatidis/snippets-service,Osmose/snippets-service,mozilla/snippets-service,mozilla/snippets-service,schalkneethling/snippets-service,mozilla/snippets-service,schalkneethling/snippets-service,glogiotatidis/snippets-service,glogiotatidis/snippets-service,schalkneethling/snippets-service,akatsoulas/snippets-service,Osmose/snippets-service,akatsoulas/snippets-service,schalkneethling/snippets-service,mozmar/snippets-service,akatsoulas/snippets-service,mozmar/snippets-service,akatsoulas/snippets-service