INSTALL: use existing shell scripts as example

Script git-pull.sh has been removed in commit [1].  Use command
"request-pull" as an example of a shell script instead.  Recently, many
of shell script commands have been re-written in C, so tweak the wording
of the sentence, while we're here.

[1]: b1456605c2 (pull: remove redirection to git-pull.sh, 2015-06-18)

Signed-off-by: Andrei Rybak <rybak.a.v@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

INSTALL

@@ -116,8 +116,8 @@ Issues of note:
 
 	- "ssh" is used to push and pull over the net.
 
-	- A POSIX-compliant shell is required to run many scripts needed
-	  for everyday use (e.g. "bisect", "pull").
+	- A POSIX-compliant shell is required to run some scripts needed
+	  for everyday use (e.g. "bisect", "request-pull").
 
 	- "Perl" version 5.8 or later is needed to use some of the
 	  features (e.g. preparing a partial commit using "git add -i/-p",