Documentation: Fix mark-up of lines with more than one tilde

The manual pages of cherry-pick and revert had examples with two revisions
on the same line in the examples section, that looked like this:

    git cherry-pick master~4 master~2::

Unfortunately, this is taken as a mark-up to make the part between two
tildes, "4 master", subscript.  Use {tilde} to make it explicit that we
do want ~ characters in these places (backslash does not help).

Reported-by: Sylvain Rabot <sylvain.rabot@f-secure.com>
Helped-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-cherry-pick.txt

@@ -92,7 +92,7 @@ git cherry-pick ^HEAD master::
 	Apply the changes introduced by all commits that are ancestors
 	of master but not of HEAD to produce new commits.
 
-git cherry-pick master\~4 master~2::
+git cherry-pick master{tilde}4 master{tilde}2::
 
 	Apply the changes introduced by the fifth and third last
 	commits pointed to by master and create 2 new commits with

Documentation/git-revert.txt

@@ -87,7 +87,7 @@ git revert HEAD~3::
 	Revert the changes specified by the fourth last commit in HEAD
 	and create a new commit with the reverted changes.
 
-git revert -n master\~5..master~2::
+git revert -n master{tilde}5..master{tilde}2::
 
 	Revert the changes done by commits from the fifth last commit
 	in master (included) to the third last commit in master