Add documentation for namespaces

[allspiritseve]

No description provided.

[anilmaurya]

Thank you @allspiritseve for contributing .

Recently AASM added namespace for events method #476 which makes this PR little outdated, Can you update docs ?

[allspiritseve]

@anilmaurya not sure what all was outdated, but I updated the example to change review_status events: approve_review => approve and unapprove_review => unapprove since events now get aliased automatically.

Let me know if you'd like any other changes.

[anilmaurya]

@allspiritseve Thank you ♡