add code comments

Example.md

@@ -9,17 +9,33 @@ var pg = require('pg');
 var conString = "postgres://postgres:1234@localhost/postgres";
 
 var server = http.createServer(function(req, res, next) {
+
+  // get a pg client from the connection pool
   pg.connect(conString, function(err, client, done) {
+
     var handleError = function(err) {
+      // no error occurred, continue with the request
       if(!err) return false;
+
+      // an error occurred, remove the client from the connection pool
       done(client);
       next(err);
       return true;
     };
+    
+    // record the visit
     client.query('INSERT INTO visit (date) VALUES ($1)', [new Date()], function(err, result) {
+      
+      // handle an error from the query
       if(handleError(err)) return;
+
+      // get the total number of visits today (including the current visit)
       client.query('SELECT COUNT(date) AS count FROM visit', function(err, result) {
+
+        // handle an error from the query
         if(handleError(err)) return;
+
+        // return the client to the connection pool for other requests to use
         done();
         res.writeHead(200, {'content-type': 'text/html'});
         res.end('You are visitor number ' + result.rows[0].count);