Add doc about migrate tasks to node10 (#15464)
Add doc about migrate tasks to node10 (#15464)

* add doc


* fix quoters

Co-authored-by: annaOpareva <84b077f88bb60125589889abec01d0df8ac4df2e@microsoft.com>
Co-authored-by: Alexander Smolyakov <3c63400f7f514ee43156049d9db0b17588f6c667@microsoft.com>
Microsoft/vsts-tasks,Microsoft/vsts-tasks,Microsoft/vso-agent-tasks,Microsoft/vso-agent-tasks,Microsoft/vsts-tasks,Microsoft/vsts-tasks,Microsoft/vsts-tasks,Microsoft/vso-agent-tasks