v.in.ogr manual: added snapping warning to WARNINGS section

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@60027 15284696-431f-4ddb-bdfa-cd5b030d7da7

vector/v.in.ogr/v.in.ogr.html

@@ -283,6 +283,13 @@ smaller value so that all areas are imported. Otherwise tiny areas are
 filtered out during import (useful to polish digitization errors or
 non-topological data).
 
+<p>
+If a message like &quot;Try to import again, snapping with at least
+1e-008: 'snap=1e-008'&quot; appears, then the map to be imported
+contains topological errors. The message suggests a value for the
+<em>snap</em> parameter to be tried. For more details, see above in
+<em><a href="v.in.ogr.html#topology-cleaning">Topology Cleaning</a></em>.
+
 <h2>ERROR MESSAGES</h2>
 
 <dl>