docs: reference libraries-bom in docs (#9)

Author: athakor

README.md

@@ -15,9 +15,27 @@ Java idiomatic client for [Cloud Memorystore for Redis][cloud-redis].
 
 Quickstart
 ----------
+If you are using Maven with a BOM, add this to your pom.xml file.
+```xml
+<dependencyManagement>
+ <dependencies>
+ <dependency>
+ <groupId>com.google.cloud</groupId>
+ <artifactId>libraries-bom</artifactId>
+ <version>2.8.0</version>
+ <type>pom</type>
+ <scope>import</scope>
+ </dependency>
+ </dependencies>
+</dependencyManagement>
 
+<dependency>
+ <groupId>com.google.cloud</groupId>
+ <artifactId>google-cloud-redis</artifactId>
+</dependency>
+```
 [//]: # ({x-version-update-start:google-cloud-redis:released})
-Add this to your pom.xml file
+If you are using Maven without a BOM, add this to your dependencies.
 ```xml
 <dependency>
  <groupId>com.google.cloud</groupId>