Update VMSS planned maintenance description to refer to best practices doc

[pratnala]

This checklist is used to make sure that common issues in a pull request are addressed. This will expedite the process of getting your pull request merged and avoid extra work on your part to fix issues discovered during the review process.

PR information

• The title of the PR is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For information on cleaning up the commits in your pull request, see this page.
• Except for special cases involving multiple contributors, the PR is started from a fork of the main repository, not a branch.
• If applicable, the PR references the bug/issue that it fixes.
• Swagger files are correctly named (e.g. the api-version in the path should match the api-version in the spec).

Quality of Swagger

• I have read the contribution guidelines.
• My spec meets the review criteria:
  • The spec conforms to the Swagger 2.0 specification.
  • The spec follows the guidelines described in the Swagger checklist document.
  • Validation tools were run on swagger spec(s) and have all been fixed in this PR.

[AutorestCI]

Automation for azure-sdk-for-go

Encountered a Subprocess error: (azure-sdk-for-go)

Command: ['/usr/local/bin/autorest', '/tmp/tmp8_oq_qoc/rest/specification/compute/resource-manager/readme.md', '--go', '--go-sdk-folder=/tmp/tmp8_oq_qoc/src/github.com/Azure/azure-sdk-for-go', '--multiapi', '--use=@microsoft.azure/autorest.go@~2.1.105', '--use-onever', '--verbose']
Finished with return code 1
and output:

AutoRest code generation utility [version: 2.0.4280; node: v8.11.3]
(C) 2018 Microsoft Corporation.
https://aka.ms/autorest
   Loading AutoRest core      '/root/.autorest/@microsoft.azure_autorest-core@2.0.4280/node_modules/@microsoft.azure/autorest-core/dist' (2.0.4280)
   Loading AutoRest extension '@microsoft.azure/autorest.go' (~2.1.105->2.1.105)
   Loading AutoRest extension '@microsoft.azure/autorest.modeler' (2.3.38->2.3.38)
Processing batch task - {"tag":"package-2018-04"} .
FATAL: System.InvalidOperationException: Swagger document contains two or more x-ms-enum extensions with the same name 'StorageAccountTypes' and different values: Standard_LRS,Premium_LRS vs. Standard_LRS,Premium_LRS,StandardSSD_LRS
   at AutoRest.Modeler.ObjectBuilder.BuildServiceType(String serviceTypeName, Boolean required) in C:\Users\ci\AppData\Local\Temp\PUBLISH8kiit\38_20171116T010915\autorest.modeler\src\ObjectBuilder.cs:line 147
   at AutoRest.Modeler.SchemaBuilder.ParentBuildServiceType(String serviceTypeName, Boolean required) in C:\Users\ci\AppData\Local\Temp\PUBLISH8kiit\38_20171116T010915\autorest.modeler\src\SchemaBuilder.cs:line 204
   at AutoRest.Modeler.SchemaBuilder.BuildServiceType(String serviceTypeName, Boolean required) in C:\Users\ci\AppData\Local\Temp\PUBLISH8kiit\38_20171116T010915\autorest.modeler\src\SchemaBuilder.cs:line 46
   at AutoRest.Modeler.SchemaBuilder.BuildServiceType(String serviceTypeName, Boolean required) in C:\Users\ci\AppData\Local\Temp\PUBLISH8kiit\38_20171116T010915\autorest.modeler\src\SchemaBuilder.cs:line 131
   at AutoRest.Modeler.SchemaBuilder.BuildServiceType(String serviceTypeName, Boolean required) in C:\Users\ci\AppData\Local\Temp\PUBLISH8kiit\38_20171116T010915\autorest.modeler\src\SchemaBuilder.cs:line 131
   at AutoRest.Modeler.SwaggerModeler.BuildCompositeTypes() in C:\Users\ci\AppData\Local\Temp\PUBLISH8kiit\38_20171116T010915\autorest.modeler\src\SwaggerModeler.cs:line 271
   at AutoRest.Modeler.SwaggerModeler.Build(ServiceDefinition serviceDefinition) in C:\Users\ci\AppData\Local\Temp\PUBLISH8kiit\38_20171116T010915\autorest.modeler\src\SwaggerModeler.cs:line 66
   at AutoRest.Modeler.Program.<ProcessInternal>d__2.MoveNext() in C:\Users\ci\AppData\Local\Temp\PUBLISH8kiit\38_20171116T010915\autorest.modeler\src\Program.cs:line 60
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at NewPlugin.<Process>d__15.MoveNext()
FATAL: go/imodeler1 - FAILED
FATAL: Error: Plugin imodeler1 reported failure.
Process() cancelled due to exception : Plugin imodeler1 reported failure.
Failure during batch task - {"tag":"package-2018-04"} -- Error: Plugin imodeler1 reported failure..
  Error: Plugin imodeler1 reported failure.

[AutorestCI]

Automation for azure-sdk-for-python

The initial PR has been merged into your service PR:
Azure/azure-sdk-for-python#2487

[AutorestCI]

Automation for azure-sdk-for-ruby

The initial PR has been merged into your service PR:
Azure/azure-sdk-for-ruby#1422

[AutorestCI]

Automation for azure-sdk-for-node

The initial PR has been merged into your service PR:
Azure/azure-sdk-for-node#2710

[AutorestCI]

Automation for azure-sdk-for-java

The initial PR has been merged into your service PR:
Azure/azure-sdk-for-java#2165

[sergey-shandar]

@hyonholee @huangpf please, review the change.

[huangpf]

LGTM

[huangpf]

LGTM