patch 8.2.2675: directory change in a terminal window shell is not followed

Problem:    Directory change in a terminal window shell is not followed.
Solution:   Add the 'autoshelldir' option. (closes #6290)
diff --git a/runtime/doc/quickref.txt b/runtime/doc/quickref.txt
index c0a070d..ead42f9 100644
--- a/runtime/doc/quickref.txt
+++ b/runtime/doc/quickref.txt
@@ -605,6 +605,7 @@
 'ambiwidth'	  'ambw'    what to do with Unicode chars of ambiguous width
 'antialias'	  'anti'    Mac OS X: use smooth, antialiased fonts
 'autochdir'	  'acd'     change directory to the file in the current window
+'autoshelldir'	  'asd'     change directory to the shell's current directory
 'arabic'	  'arab'    for Arabic as a default second language
 'arabicshape'	  'arshape' do shaping for Arabic characters
 'autoindent'	  'ai'	    take indent for new line from previous line