Add specific version for npm install command

README.md

@@ -15,7 +15,7 @@ The `erc20` contracts (both within `solidity_contracts` and `antelope_contracts`
   + Used to compile the .sol files. 
   + We chose to use solcjs because it is more actively maintained than the solc available from the package manager.
     * First install node.js and npm.
-    * Then install solcjs: `npm install -g solc`
+    * Then install solcjs: `npm install -g solc@0.8.21`
   + Make sure to install version 0.8.21.
     * Confirm with `solcjs --version`. You should get `0.8.21+commit.d9974bed.Emscripten.clang`
 - Install `jq` used to compile solidity contracts