runtime(termdebug): improve window handling, shorten var types

closes #13474

Signed-off-by: shane.xb.qian <shane.qian@foxmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/terminal.txt b/runtime/doc/terminal.txt
index f17221e..d7cfb1b 100644
--- a/runtime/doc/terminal.txt
+++ b/runtime/doc/terminal.txt
@@ -1487,7 +1487,10 @@
 	let g:termdebug_config['disasm_window_height'] = 15
 If there is no g:termdebug_config you can use: >
 	let g:termdebug_disasm_window = 15
-Any value greater than 1 will set the Asm window height to that value.
+Any value greater than 1 will set the Asm window height to that value.  
+If the current window has enough horizontal space, it will be vertically split
+and the Asm window will be shown side by side with the source code window (and
+the height option won't be used).
 
 						*termdebug_variables_window*
 If you want the Var window shown by default, set the "variables_window" flag
@@ -1498,6 +1501,9 @@
 If there is no g:termdebug_config you can use: >
 	let g:termdebug_variables_window = 15
 Any value greater than 1 will set the Var window height to that value.
+If the current window has enough horizontal space, it will be vertically split
+and the Var window will be shown side by side with the source code window (and
+the height options won't be used).
 
 Communication ~
 						*termdebug-communication*