Add URL format hint to connection form

static/css/app.css

@@ -368,8 +368,12 @@
 
 .connection-settings form {
   background: #fff;
-  padding: 40px 25px;
+  padding: 45px 25px;
   border-radius: 4px;
   -moz-border-radius: 4px;
   -webkit-border-radius: 4px;
+}
+
+.connection-settings form p.help-block {
+  font-size: 12px;
 }

static/index.html

@@ -71,7 +71,8 @@
       <form role="form" id="connection_form">
         <div class="form-group">
           <label>Enter server URL scheme</label>
-          <input type="text" class="form-control" id="connection_url" placeholder="postgres://user:password@host:port/db">
+          <input type="text" class="form-control" id="connection_url">
+          <p class="help-block">URL format: postgres://user:password@host:port/db</p>
         </div>
 
         <div class="form-group">