content: Adding final steps for voluntary exit

[0xdcota]

Tutorial title
In the existing docs here for voluntary-exit the final steps and ways to visualize the time to execute the withdrawal is missing.

Tutorial description

This issue suggest to add to main points:

• How to check when you can withdraw your exited amount.
• What function to call once the withdrawal is available.

Tag your tutorial

voluntary-exit

Publication

I couldn't find any reference only to this. I also believe this differs a bit from exiting from an ethereum validator.

Skill level
Intermediate

[0xdcota]

I will create a pull request for this update.