ownable: add a notice on renounceOwnership

[come-maiz]

🚀 Description

I added a notice to warn users calling renounceOwnership.

• 📘 I've reviewed the OpenZeppelin Contributor Guidelines
• ✅ I've added tests where applicable to test my new functionality.
• 📖 I've made sure that my contracts are well-documented.
• 🎨 I've run the JS/Solidity linters and fixed any issues (npm run lint:all:fix).

[k06a]

Maybe replace this line:

owner = address(0);

With this one:

delete owner;

To make things more clear

[come-maiz]

Thanks for the comment @k06a. That is not related to this PR though. Why don't you make the change and propose it in a separate PR, so we can discuss in there?

[shrugs]

nitpick: the english would flow better like:

"It will not be possible to call the functions with the onlyOwner modifier anymore."

[come-maiz]

Updated. Thanks for the review @shrugs !

[frangio]

Do we want to take extra measures to make renounceOwnership hard to call?

We can do something like add an argument to it that the user must explicitly pass. Perhaps the address of the contract itself.

[come-maiz]

I like that idea @frangio, like on github where you have to confirm that you want to delete a repo by entering the repo name. Report an issue to explore it further?

[frangio]

Opened #1000.