Add note about Debian default dbrd.conf

Debian's default drbd configuration has some enabled directives, which make the
init script throw errors. Document how to disable the defaults and thus get rid
of the errors.

Reviewed-by: imsnah

docs/install.sgml

@@ -332,6 +332,25 @@ echo drbd minor_count=64 >> /etc/modules
 modprobe drbd minor_count=64
       </screen>
 
+      <para>
+        It is also recommended that you comment out the default
+        resources in the <filename>/etc/dbrd.conf</filename> file, so
+        that the init script doesn't try to configure any drbd
+        devices. You can do this by prefixing all
+        <literal>resource</literal> lines in the file with the keyword
+        <literal>skip</literal>, like this:
+      </para>
+
+      <screen>
+skip resource r0 {
+...
+}
+
+skip resource "r1" {
+...
+}
+      </screen>
+
     </sect2>
 
     <sect2>