erp5: Document port range allocation.

This description is required when requesting more than one zope partition
sharing a given IP (ex: webrunner-type setup).

software/erp5/README.rst

@@ -22,5 +22,38 @@ Included cloudooo partition is **deprecated**. It is not recommended for
 intensive usage. See the ``cloudooo`` Software Release to setup a cloudooo
 cluster, more suitable for intensive usage.
 
+Port ranges
+===========
+
+This software release assigns the following port ranges by default:
+
+  ====================  ==========
+  Partition type        Port range
+  ====================  ==========
+  memcached-persistent  2000-2009
+  memcached-volatile    2010-2019
+  cloudooo              2020-2024
+  smtp                  2025-2029
+  mariadb               2099
+  zodb                  2100-2149
+  balancer              2150-2199
+  zope                  2200-*
+  ====================  ==========
+
+Non-zope partitions are unique in an ERP5 cluster, so you shouldn't have to
+care about them as a user (but a Software Release developer needs to know
+them).
+
+Zope partitions should be assigned port ranges starting at 2200, incrementing
+by some value which depends on how many zope process you want per partition
+(see the ``port-base`` parameter in ``zope-partition-dict``).
+
+Notes to the Software Release developper: These ranges are not strictly
+defined. Not each port is actually used so one may reduce alread-assigned
+ranges if needed (ex: memcached partitions use actually fewer ports). There
+should be enough room for evolution (as between smtp and mariadb types). It is
+important to not allocate any port after 2200 as user may have assigned ports
+to his zope processes.
+
 .. _RewriteRules: http://httpd.apache.org/docs/current/en/mod/mod_rewrite.html#rewriterule
 .. _VirtualHostMonster: http://docs.zope.org/zope2/zope2book/VirtualHosting.html