Add link to NXevent_data in LoadEventNexus algorithm docs

[peterfpeterson]

Since the description of the various fields is something that is frequently repeated, add a link in the algorithm documentation. This adds a link to the text and changes the description paragraph to use semantic line breaks.

There is no associated issue.

To test:

Build the docs and test the new link in the LoadEventNexus algorithm page.

This does not require release notes because it adds a single link to the algorithm docs.

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[sf1919]

I have successfully built the documentation locally. It looks correctly formatted and all the links work. Spelling correct so happy to approve.