Point out case sensitivity in JNLP Syntax documentation

This is a request from Michael Ferrante of Oracle Forms:

Update https://docs.oracle.com/javase/tutorial/deployment/deploymentInDepth/jnlpFileSyntax.html to point out case sensitivity in JNLP syntax.

Suggested text to add to first sentence on the page:

This topic describes the syntax of the Java Network Launch Protocol (JNLP) file for rich Internet applications (RIAs). It should be noted that because the JNLP file is XML, all elements and their attributes must be entered in lower case