build.ps1 expects tfx to exist

[pabrams]

When I execute build.ps1 it seems to expect tfx-cli already is installed:

tfx : The term 'tfx' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the
spelling of the name, or if a path was included, verify that the path is correct and try again.
At C:\powerbi-azure-pipelines-extensions\build.ps1:39 char:1

• tfx extension create --overrides-file $ovverides --rev-version $Updat ...

•   + CategoryInfo          : ObjectNotFound: (tfx:String) [], CommandNotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException