patch 9.1.0934: hard to view an existing buffer in the preview window

Problem:  hard to view an existing buffer in the preview window
Solution: add the :pbuffer command (Yinzuo Jiang)

Similar as `:pedit` and `:buffer` command. `:pbuffer` edits buffer [N]
from the buffer list in the preview window.

`:pbuffer` can also open special buffer, for example terminal buffer.

closes: #16222

Signed-off-by: Yinzuo Jiang <jiangyinzuo@foxmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/index.txt b/runtime/doc/index.txt
index c595d9d..e1f68a0 100644
--- a/runtime/doc/index.txt
+++ b/runtime/doc/index.txt
@@ -1,4 +1,4 @@
-*index.txt*     For Vim version 9.1.  Last change: 2023 Jul 14
+*index.txt*     For Vim version 9.1.  Last change: 2024 Dec 15
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -1529,6 +1529,7 @@
 |:ownsyntax|	:ow[nsyntax]	set new local syntax highlight for this window
 |:packadd|	:pa[ckadd]	add a plugin from 'packpath'
 |:packloadall|	:packl[oadall]	load all packages under 'packpath'
+|:pbuffer|	:pb[uffer]	edit buffer in the preview window
 |:pclose|	:pc[lose]	close preview window
 |:pedit|	:ped[it]	edit file in the preview window
 |:perl|		:pe[rl]		execute Perl command