[qutebrowser] How to send custom header ?

[John Lane]

>> I've seen content.headers.custom but it isn't clear how to use it.
> 
> What about it isn't clear?
> It's a dictionary (mapping header names to their values) in the config.
> 

What threw me off was :help content.headers.custom leading to
qute://help/settings.html#types where the example given is this:

A dictionary of values.

When setting from a string, pass a json-like dict, e.g. {"key", "value"}.

>From which I tried: :set content.headers.custom { "Host",
"www.mysite.com" } but it didn't work.