patch 8.0.1789: BufWinEnter does not work well for a terminal window

Problem:    BufWinEnter does not work well for a terminal window.
Solution:   Do not trigger BufWinEnter when opening a terminal window.
diff --git a/runtime/doc/autocmd.txt b/runtime/doc/autocmd.txt
index c3f04cc..14cf6c4 100644
--- a/runtime/doc/autocmd.txt
+++ b/runtime/doc/autocmd.txt
@@ -469,6 +469,9 @@
 				existing buffer.  But it does happen for a
 				":split" with the name of the current buffer,
 				since it reloads that buffer.
+				Does not happen for a terminal window, because
+				it starts in Terminal-Job mode and Normal mode
+				commands won't work. Use |TerminalOpen| instead.
 							*BufWinLeave*
 BufWinLeave			Before a buffer is removed from a window.
 				Not when it's still visible in another window.