Add a picture to the directed execution model

[jyu00]

URL to the relevant guide or resource

https://quantum.cloud.ibm.com/docs/en/guides/directed-execution-model

Select all that apply

• new content request
• typo
• code bug
• out-of-date content
• broken link
• other

Describe the fix or the content request.

We introduce a lot of terminologies in this page, and I think it'd be help to have a picture to show what needs to be specified on the client side and how that maps to work done on the server side.

I'm happy to come up with a draft picture but will need someone to beautify it.

For new content requests - if the request is accepted, do you want to write the content?

(No answer)