expand Morisita NEWS

Author: jarioksa

NEWS.md

@@ -56,11 +56,14 @@
   the term in plots, but switches to `X1` _etc_ if the full name does
   not fit the graph. Tilde is stripped from the term name.
 
-* `vegdist` warns now when Morisita index is used with 0/1 integer
-  data, and handles smoothly cases when two compared rows have largest
-  integer 1 and share no species (used to be `NaN`, now is distance
-  1).  Morisita index should be used only with count data, most
-  above 1. See issue
+* `vegdist` warns now when Morisita index is used with
+  presence/absence data or when a sampling unit (row) has no counts
+  above 1. Cases when two compared rows have largest count 1 and share
+  no species are now handled smoothly (used to be `NaN`), but results
+  for 0/1 rows are unreliable. For instance, two sampling units (rows)
+  are regarded identical (distance 0) if they share any species
+  although they differ in other species. It is best to use
+  `method = "horn"` if `"morisita"` gives warnings.  See issue
   [#444](https://github.com/vegandevs/vegan/issues/444).
 
 * `adipart` can use Hill numbers 1 and 2 in additive diversity