[MIGRATION] Add note about authentication errors and server errors (#534)

Author: mojito317

MIGRATION.md

@@ -23,7 +23,19 @@ There are several ways to create a client connection in `cloudant-java-sdk`:
 1. There is no built-in pagination support for views. Examples coming soon.
 1. Replay interceptors are replaced by the [automatic retries](https://github.com/IBM/ibm-cloud-sdk-common/#automatic-retries) feature for failed requests.
 1. Error handling is not transferable from `java-cloudant` to `cloudant-java-sdk`. For more information go to the [Error handling section](https://cloud.ibm.com/apidocs/cloudant?code=java#error-handling) in our API docs.
-1. Custom HTTP client configurations in `java-cloudant` are not transferable to `cloudant-java-sdk`. For more information go to the [Configuring the HTTP client section(https://githubcom/IBM/ibm-cloud-sdk-common/#configuring-the-http-client) in the IBM Cloud SDK Common README.
+1. Custom HTTP client configurations in `java-cloudant` can be set differently in
+   `cloudant-java-sdk`. For more information go to the
+   [Configuring the HTTP client section](https://github.com/IBM/ibm-cloud-sdk-common/#configuring-the-http-client)
+   in the IBM Cloud SDK Common README.
+
+### Troubleshooting
+1. Authentication errors occur during service instantiation. For example, the code `Cloudant
+   service = Cloudant.newInstance("EXAMPLE");` will fail with `Authentication information was
+   not properly configured.` if required environment variables prefixed with `EXAMPLE` are not set.
+1. Server errors occur when running a request against the service. We suggest to
+   check server errors with
+   [`getServerInformation`](https://cloud.ibm.com/apidocs/cloudant?code=java#getserverinformation)
+   which is the new alternative of `metaInformation()`.
 
 ### POJO usage in the new library