feat: simplify development setup

Warns if .env is missing.  Combines the three docker installation
commands into one, updating the docs accordingly.

Also removes the libcimp patch as npm already has it.

config/env.js

@@ -1,7 +1,11 @@
 const path = require('path');
+const fs = require('fs');
 
 if (process.env.FREECODECAMP_NODE_ENV !== 'production') {
   const envPath = path.resolve(__dirname, '../.env');
+  if (!fs.existsSync(envPath)) {
+    throw Error('.env not found, please copy sample.env to .env.');
+  }
   require('dotenv').config({ path: envPath });
 }