show help text on withdraw page on staking to warn users of withdrawal

[dbeal-eth]

should explain

• withdrawal is not unstaking
• it takes 7 days (at least) for your funds to appear on L1
• user must run a second, L1 transaction in order to claim funds after the 7+ day grace period
• it may be advisable to use hop instead of this bridge as its more user friendly and there are not too many risks