adds notes only (on diffs btwn vlkb-api and standard siav2 api)

data-discovery/notes-siav2-vlkb-extensions.tex

+
+
+VLKB extension above standard SIAv2 has:
+
+* overlap code
+* reconstructs full URLs for cutout and merge
+* response repeats all input params to the query
+* adds subsurvey metadata
+* groups the results by (sub)surveys
+* adds mergeable (virtual) datasets
+