Added CS454 example to Envelopes notebook (#55)

* CS 454 Example

* CS 454 example added

* updated envelopes example

* Updated Example on Envelopes

* Correct spelling

* CS454 example review

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Co-authored-by: Alex Griffiths <alexander.griffiths@mottmac.com>
Co-authored-by: Colin Caprani <colin.caprani@monash.edu>
Co-authored-by: Colin Caprani <31228546+ccaprani@users.noreply.github.com>