Add protostar

[Solpatium]

Protostar allows user to:

• manage dependencies,
• compiling contracts,
• testing Cairo code in Cairo (including cheatcodes).

More features are planned (like dramatic test speed improvements). Protostar doesn't require python to run.

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.