jsdl introduction (was Re: [jsdl-wg] JSDL Schema Doc)

I am attaching a revised introduction to take into account Steve's comment below. I did a bit more rewriting though since the section was getting a bit outdated, especially after the addition of Fig.1. Comments welcome. Andrew Stephen McGough wrote:

All,

I'm sat on a train so a perfect time to comment on the document...

1) Figure 1 is great now - though it isn't referred to in the text. Perhapse at the end of the paragraph beforehand: "Figure 1 illistrates places where a JSDL document may be used within a Grid environment. It should be noted that the JSDL document should not be limited to just these situations as many others may exist.".

-- Andreas Savva Fujitsu Laboratories Ltd