doc: add note about shell quoting to revision.txt

Signed-off-by: Andreas Heiduk <asheiduk@gmail.com>
Reviewed-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/revisions.txt

@@ -7,6 +7,10 @@ syntax.  Here are various ways to spell object names.  The
 ones listed near the end of this list name trees and
 blobs contained in a commit.
 
+NOTE: This document shows the "raw" syntax as seen by git. The shell
+and other UIs might require additional quoting to protect special
+characters and to avoid word splitting.
+
 '<sha1>', e.g. 'dae86e1950b1277e545cee180551750029cfe735', 'dae86e'::
   The full SHA-1 object name (40-byte hexadecimal string), or
   a leading substring that is unique within the repository.
@@ -186,6 +190,8 @@ existing tag object.
   is matched. ':/!-foo' performs a negative match, while ':/!!foo' matches a
   literal '!' character, followed by 'foo'. Any other sequence beginning with
   ':/!' is reserved for now.
+  Depending on the given text, the shell's word splitting rules might
+  require additional quoting.
 
 '<rev>:<path>', e.g. 'HEAD:README', ':README', 'master:./README'::
   A suffix ':' followed by a path names the blob or tree