docs(snapshots): mention binary snapshot portability issues (#161)

NumPy 2.0.0 changes the way arrays with object dtype are pickled: https://numpy.org/devdocs/release/2.0.0-notes.html#highlights

docs/md/snapshots.md

@@ -18,4 +18,8 @@ pytest_plugins = [ "modflow_devtools.snapshots" ]
 
 ## Disable snapshots
 
-Snapshot comparisons can be disabled by invoked `pytest` with the `--snapshot-disable` flag.
+Snapshot comparisons can be disabled by invoked `pytest` with the `--snapshot-disable` flag.
+
+## Caveats & gotchas
+
+NumPy major versions may introduce changes to `np.save()`'s binary format, causing binary array snapshot failures for arrays with object dtypes. To avoid this, check object (e.g. string) columns explicitly and then omit them from the comparison array.