Add keyboard shortcuts about docker-paperspace HOT 1 CLOSED

Fixed in 89a5728.

Notes:

• You need to first add the file to a directory of the Docker image, remove the old notebook.json, and then move the new one to the ~/.jupyter/nbconfig/ directory. For instance:

COPY notebook.json ./
RUN rm ~/.jupyter/nbconfig/notebook.json && mv ./notebook.json ~/.jupyter/nbconfig/

For some reason, it is not possible to copy notebook.json to the nbconfig directory.

COPY notebook.json ~/.jupyter/nbconfig/notebook.json
# or
ADD notebook.json ~/.jupyter/nbconfig/notebook.json

from docker-paperspace.