Add note to README that only JS is supported

[chrisbodhi]

I wouldn't be mad if you added support for other runtimes, though. 😸

[lithin]

Hey @chrisbodhi I believe this functionality is now supported in serverless framework by default if you run sls invoke local :)

https://serverless.com/framework/docs/providers/aws/cli-reference/invoke-local/

[chrisbodhi]

Delightful! Thanks for letting me know.