Add section about gRPC version conflicts to README (#53)

* Add section about gRPC version conflicts to README

* Fix

Author: justinuang

README.md

@@ -162,6 +162,8 @@ try {
 }
 ```
 
+TIP: If you are experiencing version conflicts with gRPC, see [Version Conflicts](#version-conflicts).
+
 ## OpenCensus Tracing
 
 Cloud Bigtable client supports [OpenCensus Tracing](https://opencensus.io/tracing/),
@@ -318,6 +320,33 @@ StackdriverStatsExporter.createAndRegister(
 BigtableDataSettings.enableOpenCensusStats();
 ```
 
+## Version Conflicts
+
+google-cloud-bigtable depends on gRPC directly which may conflict with the versions brought
+in by other libraries, for example Apache Beam. This happens because internal dependencies
+between gRPC libraries are pinned to an exact version of grpc-core
+(see [here](https://github.com/grpc/grpc-java/commit/90db93b990305aa5a8428cf391b55498c7993b6e)).
+If both google-cloud-bigtable and the other library bring in two gRPC libraries that depend
+on the different versions of grpc-core, then dependency resolution will fail.
+The easiest way to fix this is to depend on the gRPC bom, which will force all the gRPC
+transitive libraries to use the same version.
+
+Add the following to your project's pom.xml.
+
+```
+    <dependencyManagement>
+      <dependencies>
+        <dependency>
+          <groupId>io.grpc</groupId>
+          <artifactId>grpc-bom</artifactId>
+          <version>1.24.1</version>
+          <type>pom</type>
+          <scope>import</scope>
+        </dependency>
+      </dependencies>
+    </dependencyManagement>
+```
+
 ## Troubleshooting
 
 To get help, follow the instructions in the [shared Troubleshooting

pom.xml

@@ -158,6 +158,7 @@
         <google.api-common.version>1.8.1</google.api-common.version>
         <google.common-protos.version>1.17.0</google.common-protos.version>
         <google.core.version>1.91.3</google.core.version>
+         <!-- make sure to update the grpc version in README -->
         <grpc.version>1.24.1</grpc.version>
         <guava.version>28.1-android</guava.version>
         <opencensus.version>0.24.0</opencensus.version>