Add Langsmith

[devalexandre]

Hi, I've created a package called langsmithgo and added it to my personal repository for testing and work.

Now, I'm wondering if we can use it in langchaingo.

Here is the repository: https://github.com/devalexandre/langsmithgo

And this is my package:
https://github.com/devalexandre/mylangchaingo

What do you think about it?