Fix Deploys. Assistant#create() Performs an Update

[metaskills]

An assistant can be modified.

https://platform.openai.com/docs/api-reference/assistants/modifyAssistant

We should made the create() function do an update if the same name is found. In this way, we can update a new deployments descriptions and instructions. Few things to remember:

• Remove tip from README about deployments and names.

[metaskills]

Fixed by #4