Clarify that fork choice runs before proposal

specs/phase0/validator.md

@@ -278,7 +278,8 @@ A validator has two primary responsibilities to the beacon chain: [proposing blo
 A validator is expected to propose a [`SignedBeaconBlock`](./beacon-chain.md#signedbeaconblock) at
 the beginning of any slot during which `is_proposer(state, validator_index)` returns `True`.
 To propose, the validator selects the `BeaconBlock`, `parent`,
-that in their view of the fork choice is the head of the chain during `slot - 1`.
+that in their view of the fork choice is the head of the chain at `slot` (_after_ applying any queued
+attestations from `slot - 1`).
 The validator creates, signs, and broadcasts a `block` that is a child of `parent`
 that satisfies a valid [beacon chain state transition](./beacon-chain.md#beacon-chain-state-transition-function).