Add info to Contributors.md to avoid Conda/Pyenv dependency conflicts (#540)

As discussed in the
[Discord](https://discord.com/channels/1038097195422978059/1038097349660135474/1060194710485995521),
adding the following instructions to help future contributors avoid
dependency conflicts if they use Conda / Pyenv on their system.

CONTRIBUTING.md

@@ -61,6 +61,12 @@ If you have a Twitter account you would like us to mention, please let us know i
 
 This project uses [Poetry](https://python-poetry.org/) as a dependency manager. Check out Poetry's [documentation on how to install it](https://python-poetry.org/docs/#installation) on your system before proceeding.
 
+❗Note: If you use `Conda` or `Pyenv` as your environment / package manager, avoid dependency conflicts by doing the following first:
+1. *Before installing Poetry*, create and activate a new Conda env (e.g. `conda create -n langchain python=3.9`)
+2. Install Poetry (see above)
+3. Tell Poetry to use the virtualenv python environment (`poetry config virtualenvs.prefer-active-python true`)
+4. Continue with the following steps.
+
 To install requirements:
 
 ```bash