chore: update plugin readme with example links (#647)

Author: mayurkale22

packages/opentelemetry-plugin-document-load/README.md

@@ -57,6 +57,8 @@ Because the browser does not send a trace context header for the initial page na
 </body>
 ```
 
+See [examples/tracer-web](https://github.com/open-telemetry/opentelemetry-js/tree/master/examples/tracer-web) for a short example.
+
 ## Useful links
 - For more information on OpenTelemetry, visit: <https://opentelemetry.io/>
 - For more about OpenTelemetry JavaScript: <https://github.com/open-telemetry/opentelemetry-js>

packages/opentelemetry-plugin-mysql/README.md

@@ -20,12 +20,32 @@ npm install --save @opentelemetry/plugin-mysql
 
 ## Usage
 
+OpenTelemetry MySQL Instrumentation allows the user to automatically collect trace data and export them to the backend of choice, to give observability to distributed systems when working with [mysql](https://www.npmjs.com/package/mysql).
+
+To load a specific plugin (**MySQL** in this case), specify it in the Node Tracer's configuration
+```js
+const { NodeTracer } = require('@opentelemetry/node');
+
+const tracer = new NodeTracer({
+  plugins: {
+    mysql: {
+      enabled: true,
+      // You may use a package name or absolute path to the file.
+      path: '@opentelemetry/plugin-mysql',
+    }
+  }
+});
+```
+
+To load all the [supported plugins](https://github.com/open-telemetry/opentelemetry-js#plugins), use below approach. Each plugin is only loaded when the module that it patches is loaded; in other words, there is no computational overhead for listing plugins for unused modules.
 ```js
-const opentelemetry = require('@opentelemetry/plugin-mysql');
+const { NodeTracer } = require('@opentelemetry/node');
 
-// TODO: DEMONSTRATE API
+const tracer = new NodeTracer();
 ```
 
+See [examples/mysql](https://github.com/open-telemetry/opentelemetry-js/tree/master/examples/mysql) for a short example.
+
 ## Useful links
 - For more information on OpenTelemetry, visit: <https://opentelemetry.io/>
 - For more about OpenTelemetry JavaScript: <https://github.com/open-telemetry/opentelemetry-js>

packages/opentelemetry-plugin-redis/README.md

@@ -44,7 +44,7 @@ const { NodeTracer } = require('@opentelemetry/node');
 const tracer = new NodeTracer();
 ```
 
-<!-- See [examples/redis](https://github.com/open-telemetry/opentelemetry-js/tree/master/examples/redis) for a short example. -->
+See [examples/redis](https://github.com/open-telemetry/opentelemetry-js/tree/master/examples/redis) for a short example.
 
 ## Useful links
 - For more information on OpenTelemetry, visit: <https://opentelemetry.io/>

packages/opentelemetry-plugin-xml-http-request/README.md

@@ -25,7 +25,7 @@ const webTracerWithZone = new WebTracer({
   scopeManager: new ZoneScopeManager(),
   plugins: [
     new XMLHttpRequestPlugin({
-      propagateTraceHeaderCorsUrls: ['http://localhost:8090']    
+      propagateTraceHeaderCorsUrls: ['http://localhost:8090']
     })
   ]
 });
@@ -43,6 +43,8 @@ req.send();
 ![Screenshot of the running example](images/request.jpg)
 ![Screenshot of the running example](images/cors.jpg)
 
+See [examples/tracer-web](https://github.com/open-telemetry/opentelemetry-js/tree/master/examples/tracer-web) for a short example.
+
 ## Useful links
 - For more information on OpenTelemetry, visit: <https://opentelemetry.io/>
 - For more about OpenTelemetry JavaScript: <https://github.com/open-telemetry/opentelemetry-js>

packages/opentelemetry-shim-opentracing/README.md

@@ -34,6 +34,8 @@ opentracing.initGlobalTracer(new TracerShim(tracer));
 
 ```
 
+See [examples/opentracing-shim](https://github.com/open-telemetry/opentelemetry-js/tree/master/examples/opentracing-shim) for a short example.
+
 
 ## License