docs: document CorrelationContext propagator under Built-in Implement… (

#1080)

packages/opentelemetry-core/README.md

@@ -13,6 +13,7 @@ This package provides default implementations of the OpenTelemetry API for trace
   * [HttpTraceContext Propagator](#httptracecontext-propagator)
   * [B3 Propagator](#b3-propagator)
   * [Composite Propagator](#composite-propagator)
+  * [Correlation Context Propagator](#correlation-context-propagator)
 - [Built-in Sampler](#built-in-sampler)
   * [Always Sampler](#always-sampler)
   * [Never Sampler](#never-sampler)
@@ -55,6 +56,17 @@ const { CompositePropagator } = require("@opentelemetry/core");
 api.propagation.setGlobalPropagator(new CompositePropagator());
 ```
 
+#### Correlation Context Propagator
+Provides a text-based approach to propagate [correlation context](https://w3c.github.io/correlation-context/) to remote services using the [OpenTelemetry CorrelationContext Propagation](https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/correlationcontext/api.md#header-name) HTTP headers.
+
+```js
+const api = require("@opentelemetry/api");
+const { HttpCorrelationContext } = require("@opentelemetry/core");
+
+/* Set Global Propagator */
+api.propagation.setGlobalPropagator(new HttpCorrelationContext());
+```
+
 ### Built-in Sampler
 Sampler is used to make decisions on `Span` sampling.