Remove pygraphviz from docs

Author: christopher-wild

docs/source/installation.rst

@@ -6,16 +6,6 @@ Requirements
 CausalTestingFramework requires python version 3.9 or later
 If installing on Windows, ensure `Microsoft Visual C++ <https://docs.microsoft.com/en-us/cpp/windows/latest-supported-vc-redist>`_ is version 14.0 or greater
 
-Pygraphviz
-----------
-
-Pygraphviz can be installed through the conda-forge channel::
-
-    conda install -c conda-forge pygraphviz
-
-
-Alternatively, on Linux systems, this can be done with `sudo apt install graphviz libgraphviz-dev`.
-
 Pip Install
 -----------
 To install the Causal Testing Framework using :code:`pip` for the latest stable version::