Added headless browser section

Signed-off-by: Simon Bennetts <[email protected]>

Author: psiinon

addOns/help/src/main/javahelp/contents/releases/2_8_0.html

@@ -62,6 +62,9 @@ <h3>-dir &lt;dir&gt;</h3>
 To prevent add-ons (inadvertently) use/override core files ZAP will no longer start (and show an error) if the home and the
 installation directories are the same.
 
+<H2>Headless Browser Support</H2>
+Headless browsers are now supported by the Selenium add-on and the add-ons that use it. Both the Ajax Spider and the DOM XSS scan rule now default to headless Firefox.
+
 <h3>CA Certificate Handling</h3>
 The following options allow the root CA certificate to be set and read:
 <pre>