doc: Fix XML_CATALOG_FILES env var for Apple M1 machines

Homebrew changed the prefix for Apple M1 based machines, so our
advice for XML_CATALOG_FILES needs to mention both.  More info
on the Homebrew change can be found at:

  https://github.com/Homebrew/brew/issues/9177

Author: Julien Rouhaud 
Discussion: https://postgr.es/m/20230327082441.h7pa2vqiobbyo7rd@jrouhaud

diff --git a/doc/src/sgml/docguide.sgml b/doc/src/sgml/docguide.sgml
index cf8c072a49cd3eee62ba417e4ef82bbee556633e..599c8e62ea2ce155c2364f7f1fa0646a829b8052 100644 (file)
--- a/doc/src/sgml/docguide.sgml
+++ b/doc/src/sgml/docguide.sgml
@@ -209,9 +209,13 @@ brew install docbook docbook-xsl libxslt fop
 
    
     The Homebrew-supplied programs require the following environment variable
-    to be set:
+    to be set.  For Intel based machines, use this:
 
 export XML_CATALOG_FILES=/usr/local/etc/xml/catalog
+
+    On Apple M1 based machines, use this:
+
+export XML_CATALOG_FILES=/opt/homebrew/etc/xml/catalog
 
     Without it, xsltproc will throw errors like this: