Enhancement | Document how to add a new account after creating the landing zone

[Franr]

Add it as a section called adding new accounts, in the post-deployment page.
https://leverage.binbash.com.ar/first-steps/post-deployment/#next-steps

Reference: https://github.com/binbashar/le-tf-infra-aws/tree/master/management/global/organizations

Also add notes regarding the requirement of run tf init -reconfigure once you want to handle states created by the bootstrap user, with another user/role.

[exequielrafaela]

@Franr I'm also adding a reference to our latest related discussion => https://binbashar.slack.com/archives/GG0PJ78J3/p1678314964431729