Add SRI to script tags in README.md

[jacopotediosi]

Hi everyone!
IMHO security is important and sometimes an understimate topic.

I noticed that in README.md script tags don't include SRI hashes (https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity), so maybe many web devs who are in a hurry are copying and pasting them missing this basic security feature (I was going to do it too).

Since the effort to fix in this case is really minimal (simpy add SRI to script tags in README.md file), I open this issue to ask if my question could be compatible with the purposes of this project and to hear what the community thinks about that.

I know that the chartjs documentation itself also suffers from this problem (e.g. https://www.chartjs.org/docs/latest/getting-started/), but for that I will open a separate issue on the correct repository.