Improve upgradeability section

[maurelian]

This post from our friends at Trail of Bits made reference to some outdated content in our best practices.

It definitely needs to be revisited, and in the shorter term, possibly removed or wrapped in a big fat caveat.

[shayanb]

No links from the mentioned post to Best practices exist at this time.

Related section: https://consensys.github.io/smart-contract-best-practices/software_engineering/

[maurelian]

They took it down.... but we should definitely discuss that section's value.

[kadenzipfel]

Here are some great resources on the topic:

https://blog.openzeppelin.com/proxy-patterns/
https://blog.openzeppelin.com/towards-frictionless-upgradeability/
https://blog.openzeppelin.com/upgradeability-using-unstructured-storage/

[maurelian]

I think the right way to handle this is:

1. Write a paragraph about the risks and arugments against upgradability
2. Link to other resources such as those from Zepp and ToB above.

[fodisi]

Hi,
I'm serving as a Fellow Mentor in the Consensys Academy Blockchain Developer program, and I found this open issue while writing something for the Academy regarding upgradeability.

I just submitted PR #244 with a proposal. I'm fully open to rework it based on the community feedback so we can improve this section.

Thank you.

[shayanb]

merged in #164