Document method identifiers in Vyper compile details

[PaulRBerg]

Is your feature request related to a problem? Please describe.
The Vyper compile details do not contain information about the method identifiers (also known as function hashes).

Whereas the Solidity compile details do offer this information.

Describe the solution you'd like

Offer the method identifiers in the Vyper compile.

[Aniket-Engg]

cc: @joeizang