change `collection` to `createCollection` in README sample code

[hemidactylus]

The lines in the README sample code

// Create a collection
const collection = await astraDb.collection(COLLECTION_NAME);

seem to be incorrect, as that method does not create a collection rather returns a reference to an existing one.

Creating a collection, in my understanding, is done through createCollection with the (possible, but required for vector coll.s) addition of some parameters.

[alexleventer]

This is resolved, closing