Add Cosmos: Lightweight local block explorer

[justmert]

Added a new section for Block Explorers with a link to a Cosmos block explorer.

Checklist

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