Update zstash check docs (#368)

Author: forsyth2

docs/source/usage.rst

@@ -62,7 +62,7 @@ Local tar files as well as the sqlite3 index database (index.db) will be stored
 under ``<local path>/zstash``.
 
 **After you run** ``zstash create`` **it's highly recommended that you
-run** ``zstash check``, **detailed in the section below.**
+run** ``zstash check``, **detailed in the section below. This will allow you to check that your archival completed successfully. Do not delete any data until you've run** ``zstash check``.
 
 Basic example
 -------------