Update start.ipynb (#6342)

* Update start.ipynb

Update the start notebook with the new start notebook that details how to run against our hardware. Notably, only people with access can run circuits against our hardware.

* Update start.ipynb

lint

* Update start.ipynb

attach --pre flag to cirq install for stable version

* Update start.ipynb

Put in default value for processor_id

* Update start.ipynb

add Black as default. This _shouldn't_ run against actual hardware since a valid project_id is never specified. A valid `processor_id` however is needed to pass the CI.

* Update start.ipynb

populate default project_id

* set virtual=True to pass CI check

* Update start.ipynb

make default processor_id an empty string now that `virtual=True` is set

* Update start.ipynb

add back processor_id so it matches current merged version

* Update start.ipynb

rm `cirq --pre` install

* Update start.ipynb

delete overriding instance of `engine`

* Update start.ipynb

fix

* Update start.ipynb

nit

* Update start.ipynb

Add back original fix to known issue nteract/papermill#519

* Update start.ipynb

resolve nit

Author: senecameeks