docs: Install langsmith from conda-forge (#13335)

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langsmith is available on conda-forge as well and also a dependency of
the package so it gets installed either way by conda
https://github.com/conda-forge/langchain-feedstock/blob/306ed13308c051716ced37a28962a0ac80a9aa7f/recipe/meta.yaml#L43

README.md

@@ -30,7 +30,7 @@ pip install langchain
 
 With conda:
 ```bash
-pip install langsmith && conda install langchain -c conda-forge
+conda install langchain -c conda-forge
 ```
 
 ## 🤔 What is LangChain?