patch 8.2.0320: no Haiku support

Problem:    No Haiku support.
Solution:   Add support for Haiku. (Emir Sari, closes #5605)
diff --git a/runtime/doc/gui.txt b/runtime/doc/gui.txt
index 93e01ef..1a38496 100644
--- a/runtime/doc/gui.txt
+++ b/runtime/doc/gui.txt
@@ -99,6 +99,7 @@
 			    or $VIM/_gvimrc
 	Amiga		    s:.gvimrc, home:.gvimrc, home:vimfiles:gvimrc
 			    or $VIM/.gvimrc
+	Haiku	            $HOME/config/settings/vim/gvimrc
 
 The personal initialization files are searched in the order specified above
 and only the first one that is found is read.