display a hint when version filtering is in effect

due the use of --min or NVM_MIN, which would show only the versions
higher than the specified min version, and/or the available minor/patch
updates for the installed versions.

nvm.sh

@@ -1929,6 +1929,10 @@ BEGIN {
     print output[n]
   }
 
+  if (rows > --m) {
+    printf("[INFO] showing %d (of %d) versions.\n", m, rows) > "/dev/stderr"
+  }
+
   exit
 }'
 }