feat(extension-logging): add documentation to README

extensions/logging/README.md

@@ -34,6 +34,74 @@ In the constructor, add the component to your application:
 this.component(LoggingComponent);
 ```
 
+The component contributes bindings with keys listed below:
+
+- LoggingBindings.FLUENT_SENDER - A fluent sender
+- LoggingBindings.WINSTON_LOGGER - A winston logger
+- LoggingBindings.WINSTON_TRANSPORT_FLUENT - A fluent transport for winston
+
+The fluent sender and transport for winston can be configured against
+`LoggingBindings.FLUENT_SENDER`:
+
+```ts
+import {LoggingBindings} from '@loopback/extension-logging';
+
+app.configure(LoggingBindings.FLUENT_SENDER).to({
+  host: process.env.FLUENTD_SERVICE_HOST || 'localhost',
+  port: +(process.env.FLUENTD_SERVICE_PORT_TCP || 0) || 24224,
+  timeout: 3.0,
+  reconnectInterval: 600000, // 10 minutes
+});
+```
+
+The winston logger can be configured against `LoggingBindings.WINSTON_LOGGER`:
+
+```ts
+import {LoggingBindings} from '@loopback/extension-logging';
+
+ctx.configure<LoggerOptions>(LoggingBindings.WINSTON_LOGGER).to({
+  level: 'info',
+  format: format.json(),
+  defaultMeta: {framework: 'LoopBack'},
+});
+```
+
+The winston logger accepts two types of extensions to the following extension
+points:
+
+- WINSTON_TRANSPORT = 'logging.winston.transport'
+- WINSTON_FORMAT = 'logging.winston.format'
+
+```ts
+import {extensionFor} from '@loopback/core';
+import {format} from 'winston';
+import {WINSTON_FORMAT, WINSTON_TRANSPORT} from '@loopback/extension-logging';
+
+const myFormat: Format = ...;
+
+ctx
+  .bind('logging.winston.formats.myFormat')
+  .to(myFormat)
+  .apply(extensionFor(WINSTON_FORMAT));
+ctx
+  .bind('logging.winston.formats.colorize')
+  .to(format.colorize())
+  .apply(extensionFor(WINSTON_FORMAT));
+```
+
+## Start fluentd as a Docker container for testing
+
+For mocha tests, we use
+[testcontainers](https://github.com/testcontainers/testcontainers-node) to
+start/stop the fluentd docker container automatically.
+
+There are also scripts in `fixtures` directory:
+
+- start-fluentd.sh
+- stop-fluentd.sh
+
+The fluentd configuration is read from `fixtures/etc/fluentd.conf`.
+
 ## Contributions
 
 - [Guidelines](https://github.com/strongloop/loopback-next/blob/master/docs/CONTRIBUTING.md)