Express API has the option for custom texts, but the resulting message has no reference back to the signing. In the default template a shortened url to the signing-portal is included.
We should have the option to template this into the text that we specify.
E.g:
"Hello customer of company ABC, please follow the link to sign the agreement: ${signicatUrl}.
Thanks!"
Seems like this is already posslbe, but you fail to mention this in your docs(as far as i can see)
I can modify the following template to achieve what i want
{sender} har sendt deg dokumentet med tittelen {document-title} til signering. Velg denne lenken for å starte signeringsprosessen: {url}
Would be nice if you could list all available variables somewhere 
Hi Herman,
usage of merge fields in the API is described in the high-level product documentation here: How to create a document | Developer Pages
Additionally, you can also override all the default text strings from the developer dashboard. This is described in the following section: Custom texts | Developer Pages
Hope this was useful!