patch 9.0.0710: quitting/unloading/hiding a terminal does not work properly

Problem:    Quitting/unloading/hiding a terminal buffer does not always work
            properly.
Solution:   Avoid that ":q!" leaves an empty buffer behind.  ":bunload!" also
            kills the job and unloads the buffer.  ":hide" does not unload the
            buffer. (Yee Cheng Chin, closes #11323)
diff --git a/runtime/doc/terminal.txt b/runtime/doc/terminal.txt
index 0b94f8a..4d02558 100644
--- a/runtime/doc/terminal.txt
+++ b/runtime/doc/terminal.txt
@@ -288,9 +288,8 @@
 
 So long as the job is running the window behaves like it contains a modified
 buffer.  Trying to close the window with `CTRL-W :quit` fails.  When using
-`CTRL-W :quit!` the job is ended.  The text in the window is lost.  The buffer
-still exists, but getting it in a window with `:buffer` will show an empty
-buffer.
+`CTRL-W :quit!` the job is ended.  The text in the window is lost, the buffer
+is deleted.  With `CTRL-W :bunload!` the buffer remains but will be empty.
 
 Trying to close the window with `CTRL-W :close` also fails.   Using
 `CTRL-W :close!` will close the window and make the buffer hidden.