docs: improve gruf instrumentation documentation

instrumentation/gruf/.rubocop.yml

@@ -1,4 +1 @@
 inherit_from: ../../.rubocop.yml
-
-Style/Documentation:
-  Enabled: false

instrumentation/gruf/README.md

@@ -1,6 +1,19 @@
 # OpenTelemetry Gruf Instrumentation
 
-Todo: Add a description.
+The OpenTelemetry Gruf Ruby gem is a community-maintained instrumentation for Gruf, a gRPC framework for Ruby. It enables automatic tracing of RPC requests handled by Gruf services.
+
+## Overview
+
+This instrumentation integrates OpenTelemetry with Gruf to create spans for incoming gRPC requests. It helps in observing request flow, latency and errors in distributed systems.
+
+## How it works
+
+The Gruf instrumentation hooks into the request lifecycle of Gruf-based gRPC services and automatically creates spans for each incoming RPC request.
+
+It captures useful metadata such as:
+- RPC method name
+- Request lifecycle events
+- Errors, if any
 
 ## How do I get started?
 

instrumentation/gruf/example/controllers/example_api_controller.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 require_relative '../base'
-
+# Sample Gruf service used to demonstrate the OpenTelemetry instrumentation.
 class ExampleApiController < Gruf::Controllers::Base
   bind Proto::Example::ExampleAPI::Service
 

instrumentation/gruf/lib/opentelemetry/instrumentation/gruf/interceptors/client.rb

@@ -7,7 +7,10 @@
 module OpenTelemetry
   module Instrumentation
     module Gruf
+      # Interceptors contains the gRPC interceptors used by the Gruf instrumentation
       module Interceptors
+        # Client is a Gruf client interceptor that creates an OpenTelemetry span
+        # for each outbound gRPC call, injecting trace context into request metadata
         class Client < ::Gruf::Interceptors::ClientInterceptor
           def call(request_context:)
             return yield unless Gruf::Instrumentation.instance.installed?

instrumentation/gruf/lib/opentelemetry/instrumentation/gruf/interceptors/server.rb

@@ -7,7 +7,10 @@
 module OpenTelemetry
   module Instrumentation
     module Gruf
+      # Interceptors contains the gRPC interceptors used by the Gruf instrumentation
       module Interceptors
+        # Server is a Gruf server interceptor that creates an OpenTelemetry span
+        # for each inbound gRPC call, extracting trace context from request metadata
         class Server < ::Gruf::Interceptors::ServerInterceptor
           def call
             return yield unless Gruf::Instrumentation.instance.installed?