PATCH: document compatibility more clearly

[Peter Stephenson <p.stephenson@samsung.com>]

Probably ought to be clearer about this right at the start of the
manual, as otherwise people make (not unnatural) assumptions.

pws

diff --git a/Doc/Zsh/intro.yo b/Doc/Zsh/intro.yo
index 510a7bd..a7a2f32 100644
--- a/Doc/Zsh/intro.yo
+++ b/Doc/Zsh/intro.yo
@@ -38,8 +38,13 @@ sect(Description)
 )\
 Zsh is a UNIX command interpreter (shell) usable as an interactive
 login shell and as a shell script command processor.  Of the standard shells,
-zsh most closely resembles bf(ksh) but includes many enhancements.  Zsh
-has command line editing, builtin spelling correction, programmable
+zsh most closely resembles bf(ksh) but includes many enhancements.  It
+does not provide compatibility with POSIX or other shells in its
+default operating mode:  see
+ifnzman(the section noderef(Compatibility))\
+ifzman(the section Compatibility below).
+
+Zsh has command line editing, builtin spelling correction, programmable
 command completion, shell functions (with autoloading), a history
 mechanism, and a host of other features.
 includefile(Zsh/metafaq.yo)\x01