Add docs for gRPC library instrumentation (#6981)

Fixes #6980

instrumentation/grpc-1.6/library/README.md

@@ -0,0 +1,45 @@
+# Library Instrumentation for gRPC 1.6.0+
+
+Provides OpenTelemetry instrumentation for [gRPC](https://grpc.io/).
+
+## Quickstart
+
+### Add the following dependencies to your project:
+
+Replace `OPENTELEMETRY_VERSION` with the [latest release](https://search.maven.org/search?q=g:io.opentelemetry.instrumentation%20AND%20a:opentelemetry-grpc-1.6).
+
+For Maven, add the following to your `pom.xml` dependencies:
+
+```xml
+<dependencies>
+  <dependency>
+    <groupId>io.opentelemetry.instrumentation</groupId>
+    <artifactId>opentelemetry-grpc-1.6</artifactId>
+    <version>OPENTELEMETRY_VERSION</version>
+  </dependency>
+</dependencies>
+```
+
+For Gradle, add the following to your dependencies:
+
+```groovy
+implementation("io.opentelemetry.instrumentation:opentelemetry-grpc-1.6:OPENTELEMETRY_VERSION")
+```
+
+### Usage
+
+The instrumentation library provides the implementation of `ClientInterceptor` and `ServerInterceptor` to provide OpenTelemetry-based spans and context propagation.
+
+```java
+// For client-side, attach the interceptor to your channel builder.
+void configureClientInterceptor(Opentelemetry opentelemetry, NettyChannelBuilder nettyChannelBuilder) {
+  GrpcTelemetry grpcTelemetry = GrpcTelemetry.create(opentelemetry);
+  nettyChannelBuilder.intercept(grpcTelemetry.newClientInterceptor());
+}
+
+// For server-side, attatch the interceptor to your service.
+ServerServiceDefinition configureServerInterceptor(Opentelemetry opentelemetry, ServerServiceDefinition serviceDefinition) {
+  GrpcTelemetry grpcTelemetry = GrpcTelemetry.create(opentelemetry);
+  return ServiceInterceptors.intercept(serviceDefinition, grpcTelemetry.newServerInterceptor());
+}
+```