Install the skywater-pdk Python library into Sphinx environment.

Signed-off-by: Tim 'mithro' Ansell <tansell@google.com>

docs/environment.yml

diff --git a/docs/environment.yml b/docs/environment.yml
index c8db8b8..7100f6f 100644
--- a/docs/environment.yml
+++ b/docs/environment.yml
@@ -25,3 +25,4 @@
 # Packages installed from PyPI
 - pip:
   - -r requirements.txt
+  - ../scripts/python-skywater-pdk