more notes

README.txt

@@ -11,10 +11,17 @@ We specially care about ``selenium.webdriver.PhantomJS``, because:
 
 Things to watch out for:
 
+  - any single instance of PhantomJS acts as a single browser instance
+    that means cookies and whatnot are *shared* if you intantiate more
+    browsers for a single driver.
+    Workaround could be to start more drivers.
   - the headless browser is truly ``async``, that means an AJAX click does NOT
     wait for the AJAX request to complete, you explicitely need to wait for it
   - any single call to PhantomJS via selenium takes TIME
   - zope.testbrowser supporting methods like ``getControl`` are slow now
+  - there are 2 options for setUp/tearDown, either the driver is started and torn
+    down with the layer or with each test. Starting and stopping takes around
+    1.5-2 secs, so you decide whether you need separation or speed.
 
 WARNING
 ========