README.md in google-cloud-memcache-v1beta2-0.1.2 vs README.md in google-cloud-memcache-v1beta2-0.2.0

@@ -4,10 +4,16 @@
 
 Google Cloud Memorystore for Memcached API is used for creating and managing Memcached instances in GCP.
 
 https://github.com/googleapis/google-cloud-ruby
 
+This gem is a _versioned_ client. It provides basic client classes for a
+specific version of the Google Cloud Memorystore for Memcached API. Most users should consider using
+the main client gem,
+[google-cloud-memcache](https://rubygems.org/gems/google-cloud-memcache).
+See the section below titled *Which client should I use?* for more information.
+
 ## Installation
 
 ```
 $ gem install google-cloud-memcache-v1beta2
 ```
@@ -63,13 +69,71 @@
 end
 ```
 
 ## Supported Ruby Versions
 
-This library is supported on Ruby 2.4+.
+This library is supported on Ruby 2.5+.
 
 Google provides official support for Ruby versions that are actively supported
 by Ruby Core—that is, Ruby versions that are either in normal maintenance or
-in security maintenance, and not end of life. Currently, this means Ruby 2.4
+in security maintenance, and not end of life. Currently, this means Ruby 2.5
 and later. Older versions of Ruby _may_ still work, but are unsupported and not
 recommended. See https://www.ruby-lang.org/en/downloads/branches/ for details
 about the Ruby support schedule.
+
+## Which client should I use?
+
+Most modern Ruby client libraries for Google APIs come in two flavors: the main
+client library with a name such as `google-cloud-memcache`,
+and lower-level _versioned_ client libraries with names such as
+`google-cloud-memcache-v1beta2`.
+_In most cases, you should install the main client._
+
+### What's the difference between the main client and a versioned client?
+
+A _versioned client_ provides a basic set of data types and client classes for
+a _single version_ of a specific service. (That is, for a service with multiple
+versions, there might be a separate versioned client for each service version.)
+Most versioned clients are written and maintained by a code generator.
+
+The _main client_ is designed to provide you with the _recommended_ client
+interfaces for the service. There will be only one main client for any given
+service, even a service with multiple versions. The main client includes
+factory methods for constructing the client objects we recommend for most
+users. In some cases, those will be classes provided by an underlying versioned
+client; in other cases, they will be handwritten higher-level client objects
+with additional capabilities, convenience methods, or best practices built in.
+Generally, the main client will default to a recommended service version,
+although in some cases you can override this if you need to talk to a specific
+service version.
+
+### Why would I want to use the main client?
+
+We recommend that most users install the main client gem for a service. You can
+identify this gem as the one _without_ a version in its name, e.g.
+`google-cloud-memcache`.
+The main client is recommended because it will embody the best practices for
+accessing the service, and may also provide more convenient interfaces or
+tighter integration into frameworks and third-party libraries. In addition, the
+documentation and samples published by Google will generally demonstrate use of
+the main client.
+
+### Why would I want to use a versioned client?
+
+You can use a versioned client if you are content with a possibly lower-level
+class interface, you explicitly want to avoid features provided by the main
+client, or you want to access a specific service version not be covered by the
+main client. You can identify versioned client gems because the service version
+is part of the name, e.g. `google-cloud-memcache-v1beta2`.
+
+### What about the google-apis-<name> clients?
+
+Client library gems with names that begin with `google-apis-` are based on an
+older code generation technology. They talk to a REST/JSON backend (whereas
+most modern clients talk to a [gRPC](https://grpc.io/) backend) and they may
+not offer the same performance, features, and ease of use provided by more
+modern clients.
+
+The `google-apis-` clients have wide coverage across Google services, so you
+might need to use one if there is no modern client available for the service.
+However, if a modern client is available, we generally recommend it over the
+older `google-apis-` clients.