fix curl command for token request

[Anika-Sol]

I tried out the token request for technical communication between two applications, which failed due to a small typo in the command: The flag data-urlencode needs to be prefixed with -- to work, see curl help:

% curl --help all | grep urlencode
--data-urlencode <data> HTTP POST data URL encoded

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[MichaelPShea]

@Anika-Sol Thanks for the feedback. I admit that I have trouble testing CURL on my Windows machine. I just want to confirm the problem and then fix the documentation.

[MichaelPShea]

Updated the documentation.