docs(loggly): added docs for loggly appender

docs/loggly.md

@@ -0,0 +1,36 @@
+# Loggly Appender
+
+Sends logging events to [Loggly](https://www.loggly.com), optionally adding tags. This appender uses [node-loggly](https://www.npmjs.com/package/loggly), and you will need to include that in your dependencies if you want to use this appender. Consult the docs for node-loggly, or loggly itself, if you want more information on the configuration options below.
+
+## Configuration
+
+* `type` - `loggly`
+* `token` - `string` - your really long input token
+* `subdomain` - `string` - your subdomain
+* `tags` - `Array<string>` (optional) - tags to include in every log message
+
+This appender will scan the msg from the logging event, and pull out any argument of the
+shape `{ tags: [] }` so that it's possible to add additional tags in a normal logging call. See the example below.
+
+## Example
+
+```javascript
+log4js.configure({
+  appenders: {
+    loggly: {
+      type: 'loggly',
+      token: 'somethinglong',
+      subdomain: 'your.subdomain',
+      tags: [ 'tag1' ]
+    }
+  },
+  categories: {
+    default: { appenders: ['loggly'], level: 'info' }
+  }
+});
+
+const logger = log4js.getLogger();
+logger.info({ tags: ['my-tag-1', 'my-tag-2'] }, 'Some message');
+```
+
+This will result in a log message being sent to loggly with the tags `tag1`, `my-tag-1`, `my-tag-2`.