restore, commit: Help += note that those tools are low-level

Suggessted by @jerome here: !19 (comment 129181)

Co-authored-with: Jérome Perrin <jerome@nexedi.com>
/reviewed-on !19

zodbtools/zodbcommit.py

@@ -173,7 +173,16 @@ On success the ID of committed transaction is printed to stdout.
 Options:
 
     -h  --help      show this help
-""", file=out)
+""" + (_low_level_note % "zodb commit"), file=out)
+
+_low_level_note = """
+Note: `%s` is low-level tool that creates transactions without checking
+data for correctness and consistency at object level. Given incorrect data it
+can create transactions with objects that cannot be unpickled, or with objects
+that reference other objects that may not already be present in the database.
+Such transactions would lead to errors later when accessing those objects at
+application level.
+"""
 
 @func
 def main(argv):

zodbtools/zodbrestore.py

@@ -24,7 +24,7 @@ ZODB storage. See Zodbdump documentation for details.
 
 from __future__ import print_function
 from zodbtools.zodbdump import DumpReader
-from zodbtools.zodbcommit import zodbcommit
+from zodbtools.zodbcommit import zodbcommit, _low_level_note
 from zodbtools.util import asbinstream, ashex, storageFromURL
 from golang import func, defer
 
@@ -64,7 +64,7 @@ On success the ID of every restored transaction is printed to stdout.
 Options:
 
     -h  --help      show this help
-""", file=out)
+""" + (_low_level_note % "zodb restore"), file=out)
 
 @func
 def main(argv):