runtime(doc): Fix typo in "Jumping to Changes", usr_08.txt

- Change "Prepended" (past tense) to "Prepend" (present tense,
  imperative).
- Add short examples clarifying the behavior of prepending a count to
  commands that jump to changes in diff mode.

closes: #18810

Signed-off-by: Brent Pappas <pappasbrent@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

Author: PappasBrent

runtime/doc/usr_08.txt

@@ -1,4 +1,4 @@
-*usr_08.txt*	For Vim version 9.1.  Last change: 2025 Nov 09
+*usr_08.txt*	For Vim version 9.1.  Last change: 2025 Nov 26
 
 
 		     VIM USER MANUAL	by Bram Moolenaar
@@ -444,7 +444,8 @@ To go the other way use: >
 
 	[c
 
-Prepended a count to jump further away.
+Prepend a count to jump further away. Thus "4]c" jumps to the fourth next
+change, and "3[c" jumps to the third previous change.
 
 
 REMOVING CHANGES