Update "write your first serverless program" guide

[abbycross]

In conversation with @acastellane - the flow of the page can be confusing, and the authentication instructions could be clearer (there may now be a better link to point to). The updates include the following:

• Include a high-level tl;dr: overview of the steps
• remind users their serverless workloads won't show up on their Workloads table
• be clear about which saved account is default (this applies not just to serverless)
• where to go to find out about package versions/dependencies (also a larger question)

[ElePT]

I am happy to help out with this content, let me know the best way I can help.

[abbycross]

Thank you @ElePT! Docs team won't have bandwidth till after QDC, but what we want to do is review the flow of the page and how it interacts with the recently-streamlined authentication instructions, as there are some possible mis-matches in what gets linked out where. If you have other thoughts or spot immediate fixes, feel free to dive in or make notes here - appreciate it!