multi-worker-process: Add multiple worker assign syntax description

docs/v1.0/multi-process-workers.txt

@@ -47,6 +47,82 @@ Some plugins don't work on multi process worker, e.g. `in_tail`. For such plugin
 
 With this directive, you can mix multi-process ready and non-multi-process ready plugins in 1 instance.
 
+### <worker N-M> directive
+
+As of Fluentd v1.4.0, `<worker N-M>` syntax has been introduced:
+
+    :::text
+    <system>
+      workers 6
+    </system>
+
+    <worker 0-1>
+      <source>
+        @type forward
+      </source>
+
+      <filter test>
+        @type record_transformer
+        enable_ruby
+        <record>
+          worker_id ${ENV['SERVERENGINE_WORKER_ID']}
+        </record>
+      </filter>
+
+      <match test>
+        @type stdout
+      </match>
+    </worker>
+    # work on worker 0 and worker 1.
+
+    <worker 2-3>
+      <source>
+        @type tcp
+        <parse>
+          @type none
+        </parse>
+        tag test
+      </source>
+
+      <filter test>
+        @type record_transformer
+        enable_ruby
+        <record>
+          worker_id ${ENV['SERVERENGINE_WORKER_ID']}
+        </record>
+      </filter>
+
+      <match test>
+        @type stdout
+      </match>
+    </worker>
+    # work on worker 2 and worker 3.
+
+    <worker 4-5>
+      <source>
+        @type udp
+        <parse>
+          @type none
+        </parse>
+        tag test
+      </source>
+
+      <filter test>
+        @type record_transformer
+        enable_ruby
+        <record>
+          worker_id ${ENV['SERVERENGINE_WORKER_ID']}
+        </record>
+      </filter>
+
+      <match test>
+        @type stdout
+      </match>
+    </worker>
+    # work on worker 4 and worker 5.
+
+With this directive, you can specify multiple workers per worker directive.
+
 ### root_dir/@id parameter
 
 These parameters must be specified when you use file buffer.