mongo-3.1 library: add README.md (#9854)

instrumentation/mongo/mongo-3.1/library/README.md

@@ -0,0 +1,50 @@
+# MongoDB library instrumentation
+
+This package contains the library to help instrument MongoDB Client.
+
+## Quickstart
+
+### Dependencies
+
+Replace OPENTELEMETRY_VERSION with the [latest release](https://central.sonatype.com/search?q=g:io.opentelemetry.instrumentation++a:opentelemetry-mongo-3.1&smo=true).
+
+For Maven, add to your `pom.xml` dependencies:
+
+```xml
+<dependencies>
+  <dependency>
+    <groupId>io.opentelemetry.instrumentation</groupId>
+    <artifactId>opentelemetry-mongo-3.1</artifactId>
+    <version>OPENTELEMETRY_VERSION</version>
+  </dependency>
+</dependencies>
+```
+
+For Gradle, add to your dependencies:
+
+```gradle
+implementation("io.opentelemetry.instrumentation:instrumentation:opentelemetry-mongo-3.1:OPENTELEMETRY_VERSION")
+```
+
+## Usage
+
+The instrumentation is initialized by passing a `MongoTelemetry::newCommandListener()` to the `MongoClientSettings` builder. You must set the `OpenTelemetry` to use with the feature.
+
+```java
+OpenTelemetry openTelemetry = initializeOpenTelemetryForMe();
+MongoTelemetry mongoTelemetry = MongoTelemetry.builder(openTelemetry).build();
+
+MongoClientSettings settings = MongoClientSettings.builder()
+    .applyConnectionString(ConnectionString("mongodb://localhost:27017"))
+    .addCommandListener(mongoTelemetry.newCommandListener())
+    .build();
+
+// With Reactive Streams
+MongoClient client = MongoClients.create(settings);
+```
+
+A logging message example produced by `LoggingSpanExporter`:
+
+```
+INFO: 'insert test.MyCollection' : 4487bebe5fcfc91af2cd517685552a33 a56685e62bf8f87c CLIENT [tracer: io.opentelemetry.mongo-3.1:1.31.0-alpha] AttributesMap{data={db.operation=insert, db.mongodb.collection=MyCollection, net.peer.port=27017, db.name=test, db.connection_string=mongodb://localhost:27017, net.peer.name=localhost, db.statement={"insert": "MyCollection", "ordered": "?", "txnNumber": "?", "$db": "?", "$clusterTime": {"clusterTime": "?", "signature": {"hash": "?", "keyId": "?"}}, "lsid": {"id": "?"}, "documents": [{"_id": "?", "name": "?", "createdAt": "?", "updatedAt": "?"}]}, db.system=mongodb}, capacity=128, totalAddedValues=8}
+```