Add Starknet by Example

[joshklop]

Add Starknet by Example.

Checklist

• [X] The URL is not already present in the list (check with CTRL/CMD+F in the raw markdown file).
• [X] Each description starts with an uppercase character and ends with a period.
  Example: cairo - The Cairo programming language.
• [X] Drop all A / An prefixes at the start of the description.
• [X] Avoid using the word StarkNet in the description. (I think the single instance of "Starknet" is warranted in this case)