Add link to the-links-object.md in the Links section of each event

[magnusbaeck]

Description

At the 2021-09-16 community protocol workshop @m-linner-ericsson suggested that we add a link to the-links-object.md at the start of the Links section of every event documentation file.

Motivation

Much easier to find the details of how to actually express a link in an event. Right now each event just documents which link types are available.

Exemplification

N/A

Benefits

Better navigation within the documentation.

Possible Drawbacks

None.