docs: adds README for node

examples/language-sdk-instrumentation/nodejs/README.md

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+## Continuous Profiling for Node applications
+### Profiling a Node Rideshare App with Pyroscope
+
+![golang_example_architecture_new_00](https://user-images.githubusercontent.com/23323466/173370161-f8ba5c0a-cacf-4b3b-8d84-dd993019c486.gif)
+
+Note: For documentation on Pyroscope's Node integration visit [our website](https://grafana.com/docs/pyroscope/latest/configure-client/language-sdks/nodejs/).
+
+## Background
+In this example, we show a simplified, basic use case of Pyroscope. We simulate a "ride share" company which has three endpoints found in `main.js`:
+- `/bike`    : calls the `bikeSearchHandler()` function to order a bike
+- `/car`     : calls the `carSearchHandler()` function to order a car
+- `/scooter` : calls the `scooterSearchHandler()` function to order a scooter
+
+We also simulate running 3 distinct servers in 3 different regions (via [docker-compose.yml](./express/docker-compose.yml))
+- us-east
+- eu-north
+- ap-south
+
+One of the most useful capabilities of Pyroscope is the ability to tag your data in a way that is meaningful to you. In this case, we have two natural divisions, and so we "tag" our data to represent those:
+- `region`: statically tags the region of the server running the code
+
+
+## Tagging static region
+Tagging something static, like the `region`, can be done in the initialization code in the `main()` function:
+```js
+  Pyroscope.init({
+    appName: 'nodejs',
+    serverAddress: process.env['PYROSCOPE_SERVER'] || 'http://pyroscope:4040',
+    tags: { region: process.env['REGION'] || 'default' }
+  });
+```
+
+## Resulting flame graph / performance results from the example
+### Running the example
+
+There are 3 examples:
+* `express` - basic integration example
+* `express-ts` - type script example
+* `express-pull` — pull mode example
+
+To use any of the examples, run the following commands:
+```shell
+# change directory
+cd express # or cd express-ts / cs express-pull
+
+# Pull latest pyroscope image:
+docker pull grafana/pyroscope:latest
+
+# Run the example project:
+docker-compose up --build
+
+# Reset the database (if needed):
+docker-compose down
+```
+
+This example runs all the code mentioned above and also sends some mock-load to the 3 servers as well as their respective 3 endpoints. If you select `nodejs.wall` from the dropdown, you should see a flame graph that looks like this (below).
+After 20-30 seconds, the flame graph updates. Click the refresh button. We see our 3 functions at the bottom of the flame graph taking CPU resources _proportional to the size_ of their respective `search_radius` parameters.