Add links to other proposals

[dead-claudia]

(Continuation/successor to #64, that's a little more actionable.)

Could you link a few other function composition proposals, to show a few other ways it could be done? Here's a few:

• Operator-based: this repo
• Function-based: this comment
• Method-based: this repo

(Shameless plug: mine is the operator variant. I'll also point out that my proposal also has an alternative for await that's more general, but that's a separate issue.)

[littledan]

Feel free to make a PR.