Update README.md

add some usage notes

examples/privatebin/README.md

@@ -1,3 +1,9 @@
 # References
 
 - https://github.com/PrivateBin/PrivateBin
+
+# Notes
+
+You have to put the example config files to your Docker volume bind mount path.
+
+Only the `config.php` is necessary for a default installation with 10 MB file upload limit. If you want to increase this upload limit, you must also use the other config files.