Clarify table creation properties vs update TTL in docs

[Raynos]

When reading the README its not obvious to me that I cannot configure TTL in the CreateTable() method.

It would be useful to clarify in updateTTL() that

• It should be done once after calling db.create(tableName, ...)
• It cannot be done in create() because updating TTL is a seperate method, documenting that will reduce confusion.

[heapwolf]

it could be done in create, its just tricky to reason about how to send non related native sdk arguments.

[Raynos]

I think the current implementaiton is good.

As a user of dynavolt i jsut didnt know that dynamodb has X metadata in Create and also 3 dangling meta that can only be applied with updateY()