Update SemVer discussion for TS

[chriskrycho]

This is currently blocked, but as part of emberjs/ember.js#20162 and the general work to implement RFC 0800: TypeScript Adoption Plan, we need to update our text about SemVer on the website to cover our TypeScript support policy and link to https://semver-ts.org. This update should land after we implement emberjs/ember.js#20185, so that our stated policy matches our actual implementation.

(I plan to do this, though others are certainly welcome to jump in!)

[chriskrycho]

No longer blocked! I'll try to open a PR in the next few days, but if someone else beats me to it I won't be sad. Done! #964. 😏