Add COPASI installation instructions to docs

Added a new section detailing how to install PyEnzyme with COPASI support using pip or uv. Included a reference to the COPASI integration guide for further information.

Author: JR-1991

docs/src/content/docs/basic/installation.mdx

@@ -78,6 +78,22 @@ uv pip install "pyenzyme[pysces]"
 
 See the [mathematical modeling guide](/basic/modelling/) for details on using PySCeS with PyEnzyme.
 
+### COPASI support (`copasi`)
+
+Enables using COPASI for kinetic modeling and parameter fitting. Installs `copasi-basico`.
+
+**With pip:**
+```bash
+pip install "pyenzyme[copasi]"
+```
+
+**With uv:**
+```bash
+uv pip install "pyenzyme[copasi]"
+```
+
+See the [COPASI integration guide](/integrations/copasi/) for details on using COPASI with PyEnzyme.
+
 ### Development dependencies (`tests`)
 
 Includes testing tools for development and running the test suite. Installs `pytest`, `pytest-httpx`, and `pytest-sugar`.