runtime(vim): don't set compiler, update a comment for vimdoc compiler (#14532)

Signed-off-by: shane.xb.qian <shane.qian@foxmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/compiler/vimdoc.vim b/runtime/compiler/vimdoc.vim
index d83b924..a30355f 100644
--- a/runtime/compiler/vimdoc.vim
+++ b/runtime/compiler/vimdoc.vim
@@ -1,9 +1,10 @@
 " Vim Compiler File
 " Language:             vimdoc
 " Maintainer:           Wu, Zhenyu <wuzhenyu@ustc.edu>
-" Latest Revision:      2024-04-09
+" Latest Revision:      2024-04-13
 "
-" you can get it by `pip install vimdoc` or the package manager of your distribution.
+" If you can not find 'vimdoc' in the package manager of your distribution e.g
+" 'pip', then you may need to build it from its source.
 
 if exists('b:current_compiler')
   finish