completions: content: small note for $ escapes

I stumbled uppon this, while not understanding why my $ in my completions were replaced with empty strings.
Then I searched trough the manual where this format with the $ is explained and how to escape it.
So i put the explanation here.

Mabye it is possible to link to the description for the content format in snippets? (I did not know how to link it)

best regards
Philipp