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/help.txt b/runtime/doc/help.txt
index 8f67ef5..f2b7846 100644
--- a/runtime/doc/help.txt
+++ b/runtime/doc/help.txt
@@ -204,6 +204,7 @@
 |os_os2.txt|	OS/2
 |os_qnx.txt|	QNX
 |os_risc.txt|	RISC-OS
+|os_haiku.txt|	Haiku
 |os_unix.txt|	Unix
 |os_vms.txt|	VMS
 |os_win32.txt|	MS-Windows