[ANN] Jupyter Notebook 6.1.0 RC1 is available

[Kevin Bates]

Hello, In preparation for the Notebook 6.1.0 release, we've decided to first deliver release candidate 1.  We would greatly appreciate it if you could take it for a spin prior to the GA release (which we'd like to make available in 3-4 weeks).

Please choose the appropriate command for your situation...

Fresh install:

`pip install notebook==6.1.0rc1 --pre`

`conda install -c conda-forge/label/notebook_rc notebook`

Update existing:

`pip install notebook==6.1.0rc1 --pre --upgrade`

`conda update -c conda-forge/label/notebook_rc notebook`