docs(changelog): add the #1580 fragment

changelog.d/1580-orbital-ground-focus.md

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+- Hold the orbital camera on a mapped site as the satellite passes over it,
+  from a click on its marker or its Live Signals row, and list nearby sites
+  and satellites in orbit's Live Signals, where a row focuses a site or rides
+  a satellite (Denis Groshev, @ZloyS, #1580).