Add examples to repo to illustrate use of "Assumption" class

[kestewart]

ELISA Arch WG Feedback (on spdx/spdx-3-model#1241)

It would be good to have examples somewhere so that what assumptions are is clear and we can also see assumptions at different level.

• Mutex assumed to be locked by caller of a function (in this case the function is the item that the assumption applies to)
• Independent watchdog assumed to trigger in case of dangerous delay (in this case the whole SW/HW stack, except the WTD itself, is the item that the assumption applies to)
• In the space industry, if an algorithm for uploading files from the ground assumes a low Earth orbit spacecraft rather than a deep space probe, both its requirements and implementation may differ significantly. In this case the item the assumption applies to is the environmental context of use of the algorithm