Added a warning to the "Open Software Release" button at the home page of the webrunner

@Tyagov 

Some screenshots:
![Screenshot_from_2017-03-24_11-54-11](/uploads/16f5901303b083dee2c771bcc77dd93b/Screenshot_from_2017-03-24_11-54-11.png)

/reviewed-on nexedi/slapos.toolbox!10

slapos/runner/templates/projectFolder.html

@@ -33,7 +33,7 @@
 	<div id="fileTree" class="file_tree"></div>
 	<div id="file_info" class="file_info">
 	<img src="{{ url_for('static', filename='images/check.png') }}" class="check" id="check" alt=""/>
-	<span id="info">Please select your project folder into the box...</span></div>
+  <p><font color="red">WARNING:</font> Opening a new software release <font color="red">WILL ERASE YOUR EXISTING INSTANCE</font>. Proceed with caution!</p></div>
 	<input type="hidden" name="path" id="path" value="" />
 	<input type="submit" name="open" id ="open" value="Open Software" class="button"/>
 </div>