docs: Mention add_pip_as_python_dependency in compatibility mode for pixi-pack (#3188)

Author: pavelzw

docs/advanced/production_deployment.md

@@ -168,3 +168,11 @@ conda env create -p ./env --file environment.yml
 
 !!!note ""
     The `environment.yml` and `repodata.json` files are only for this use case, `pixi-pack unpack` does not use them.
+
+!!!note ""
+    Both `conda` and `mamba` are always installing pip as a side effect when they install python, see [`conda`'s documentation](https://docs.conda.io/projects/conda/en/25.1.x/user-guide/configuration/settings.html#add-pip-as-python-dependency-add-pip-as-python-dependency).
+    This is not different from how `pixi` works and can lead to solver errors when using `pixi-pack`'s compatibility mode since `pixi-pack` doesn't include `pip` by default.
+    You can fix this issue in two ways:
+
+    - Add `pip` to your `pixi.lock` file using `pixi add pip`.
+    - Configuring `conda` (or `mamba`) to not install `pip` by default by running `conda config --set add_pip_as_python_dependency false` (or by adding `add_pip_as_python_dependency: False` to your `~/.condarc`)