Update WebSphere documentation to ask customers to make their WebSphere compile jsps in java 1.5

After installing JIRA on Websphere 6.1.
The file "ibm-web-ext.xmi" in the WEB-INF directory of the WAR needs to have this line added to it:
<jspAttributes xmi:id="JSPAttribute_[number]" name="jdkSourceLevel" value="15"/>
Where [number] has to be an unique integer within the file.

References:
Configuring JSP engine parameters: http://publib.boulder.ibm.com/infocenter/wasinfo/v6r0/index.jsp?topic=/com.ibm.websphere.express.doc/info/exp/ae/tweb_jspengine.html
JSP compiling problem: http://www-01.ibm.com/support/docview.wss?uid=swg21243896

Please update the docs to reflect this change.