Update readme with indication that a new js package is being worked on

[kennethcassel]

Is your feature request related to a problem? Please describe. Ran into a dependency conflict while trying to create a script which would mint NFT's and send them to a user.

Ended up finding this SO answer that describes the dependency conflict

The @metaplex/js library uses old versions of MPL packages such as @metaplex-foundation/mpl-token-metadata which, as you figured out, use an old version of @solana/spl-token. Unfortunately, if even just one nested dependency uses version 0.1.8 of the SPL token program, it will be used for the entire project.

It goes on to note that the @metaplex/js library will be depreacted

However, it is worth noting that the current JavaScript SDK from Metaplex is going to be deprecated in favour of the new one: https://github.com/metaplex-foundation/js-next

Describe the solution you'd like Update the readme to indicate that this project is likely to be deprecated in the future.