tutorials: added getting-started tutorial + relevant images

[RamonAra209]

Note: hyperlinks still need to be added/fixed. In the section labeled "Overview" if you click Job or JobSpec, the links send you to the relevant portion of the API docs, but you instantly get redirected to: https://exaworks.org/#psij-python/docs/.generated/psij.html

Accessing links from within the website documentation works fine.

[review-notebook-app[bot]]

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[mtitov]

@hategan Mihael, can you please have a look? seems like all comments are addressed