MINOR/DOC: spoe-server: Add documentation

This is the documentation and examples.
diff --git a/contrib/spoa_server/ps_lua.lua b/contrib/spoa_server/ps_lua.lua
new file mode 100644
index 0000000..2662045
--- /dev/null
+++ b/contrib/spoa_server/ps_lua.lua
@@ -0,0 +1,17 @@
+require("print_r")
+
+print_r("Load lua message processors")
+
+spoa.register_message("check-client-ip", function(args)
+	print_r(args)
+	spoa.set_var_null("null", spoa.scope.txn)
+	spoa.set_var_boolean("boolean", spoa.scope.txn, true)
+	spoa.set_var_int32("int32", spoa.scope.txn, 1234)
+	spoa.set_var_uint32("uint32", spoa.scope.txn, 1234)
+	spoa.set_var_int64("int64", spoa.scope.txn, 1234)
+	spoa.set_var_uint64("uint64", spoa.scope.txn, 1234)
+	spoa.set_var_ipv4("ipv4", spoa.scope.txn, "127.0.0.1")
+	spoa.set_var_ipv6("ipv6", spoa.scope.txn, "1::f")
+	spoa.set_var_str("str", spoa.scope.txn, "1::f")
+	spoa.set_var_bin("bin", spoa.scope.txn, "1::f")
+end)