Add spring web documentation (#914)

* instrumentation-core spring-web-3.1 README first draft

* clean up formatting

* more clean ups

* fix incorrect reference

* Update README.md

* format

* clean up readme

* Update instrumentation-core/spring/spring-web-3.1/README.md

Co-authored-by: Trask Stalnaker <trask.stalnaker@gmail.com>

Co-authored-by: Trask Stalnaker <trask.stalnaker@gmail.com>

instrumentation-core/spring/spring-web-3.1/README.md

@@ -0,0 +1,89 @@
+# Manual Instrumentation for Spring-Web
+
+Provides OpenTelemetry instrumentation for Spring's RestTemplate.
+
+## Quickstart
+
+### Add these dependencies to your project.
+
+Replace `SPRING_VERSION` with the version of spring you're using.
+`Minimum version: 3.1`
+
+Replace `OPENTELEMETRY_VERSION` with the latest stable [release](https://mvnrepository.com/artifact/io.opentelemetry).
+`Minimum version: 0.8.0`
+
+For Maven add to your `pom.xml`:
+```xml
+<dependencies>
+  <!-- opentelemetry -->
+  <dependency>
+    <groupId>io.opentelemetry.instrumentation</groupId>
+    <artifactId>opentelemetry-spring-web-3.1</artifactId>
+    <version>OPENTELEMETRY_VERSION</version>
+  </dependency>
+
+   <!-- provides opentelemetry-sdk -->
+   <dependency>
+    <groupId>io.opentelemetry</groupId>
+    <artifactId>opentelemetry-exporters-logging</artifactId>
+    <version>OPENTELEMETRY_VERSION</version>
+  </dependency>
+
+  <!-- required to instrument spring-web -->
+  <!-- this artifact should already be present in your application -->
+  <dependency>
+    <groupId>org.springframework</groupId>
+    <artifactId>spring-web</artifactId>
+    <version>SPRING_VERSION</version>
+  </dependency>
+
+</dependencies>
+```
+
+For Gradle add to your dependencies:
+```groovy
+implementation 'io.opentelemetry.instrumentation:opentelemetry-spring-web-3.1:OPENTELEMETRY_VERSION'
+implementation 'io.opentelemetry:opentelemetry-exporters-logging:OPENTELEMETRY_VERSION'
+
+//this artifact should already be present in your application
+implementation 'org.springframework:spring-web:SPRING_VERSION'
+```
+
+### Features
+
+#### RestTemplateInterceptor
+
+RestTemplateInterceptor adds OpenTelemetry client spans to requests sent using RestTemplate by implementing the [ClientHttpRequestInterceptor](https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/http/client/ClientHttpRequestInterceptor.html)
+interface. An example is shown below:
+
+##### Usage
+
+```java
+
+import io.opentelemetry.instrumentation.spring.httpclients.RestTemplateInterceptor
+import io.opentelemetry.trace.Tracer;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.http.client.ClientHttpRequestInterceptor;
+import org.springframework.web.client.RestTemplate;
+
+@Configuration
+public class RestTemplateConfig {
+
+   @Bean
+   public RestTemplate restTemplate(Tracer tracer) {
+
+      RestTemplate restTemplate = new RestTemplate();
+      RestTemplateInterceptor restTemplateInterceptor = new RestTemplateInterceptor(tracer);
+      restTemplate.getInterceptors().add(restTemplateInterceptor);
+
+      return restTemplate;
+   }
+}
+```
+
+### Starter Guide
+
+Check out the opentelemetry [quick start](https://github.com/open-telemetry/opentelemetry-java/blob/master/QUICKSTART.md) to learn more about OpenTelemetry instrumentation.