Add chat placeholder message to teach how user can show commands help

static/galene.css

@@ -329,6 +329,16 @@ textarea.form-reply {
     transition: border-color ease-in-out .15s,box-shadow ease-in-out .15s;
 }
 
+.form-reply::placeholder {
+  font-size: .8em;
+  padding-top: 2px;
+  opacity: .7;
+}
+
+.form-reply:focus::placeholder {
+  color: transparent;
+}
+
 .select {
     display: block;
     width: 100%;

static/galene.html

@@ -89,7 +89,7 @@
                   <div id="box"></div>
                   <div class="reply">
                     <form id="inputform">
-                      <textarea id="input" class="form-reply"></textarea>
+                      <textarea id="input" class="form-reply" placeholder="Type /help to show commands"></textarea>
                       <input id="inputbutton" type="submit" value="&#10148;" class="btn btn-default"/>
                     </form>
                   </div>