Adding package for solidity-mode

- A brief summary of what the package does:
  This is the language mode for the smart contracts language called
  Solidity used in the Ethereum network.

- A direct link to the package repository:
  https://github.com/ethereum/emacs-solidity

- Your association with the package (e.g., are you the maintainer? have
  you contributed? do you just like the package a lot?):
  I am the maintainer

recipes/solidity-mode

@@ -0,0 +1,3 @@
+(solidity-mode
+     :repo "ethereum/emacs-solidity"
+     :fetcher github)