Voluntary Exit page is somewhat confusing/needs improvements

[remyroy]

This is related to https://docs.teku.pegasys.tech/en/latest/HowTo/Voluntary-Exit/ .

4 things should be improved:

• The mention to having the REST API enabled is somewhat burried down below. That is confusing some users and it is somewhat critical for having a working call to the voluntary-exit command. It should be added in an Important block section or more emphasis should be added for this part since many users are likely not running with REST API enabled.
• In the example, we can see the use of the http://10.32.100.1:5051 value for the --beacon-node-api-endpoint. It's unlikely that this is going to work in the real world. A better value would be http://127.0.0.1:5051 and telling the user that this command is supposed/likely to be ran on the staking machine.
• In most cases, the --epoch flag is not going to be used. When a user wants to exit, he'll want to do it now. That flag should be removed from the example.
• The following phrase:

A voluntary exit is when a validator chooses to stop performing its duties, and exits the beacon chain.

should be changed to something like this to avoid other potential confusions:

A voluntary exit is when a validator chooses to stop performing its duties, and exits the beacon chain permanently. There is no way to rejoin the network once you do a voluntary exit. Your funds will be frozen until the withdrawal process is implemented.