add changelog

.github/CHANGELOG.md

@@ -123,6 +123,9 @@
 
 ### Documentation
 
+* Mark ``CUQUANTUM_SDK`` environment variable set as an option.
+  [(#964)](https://github.com/PennyLaneAI/pennylane-lightning/pull/964)
+
 * Update ``lightning.tensor`` documentation to include all the new features added since pull request #756. The new features are: 1, Finite-shot measurements; 2. Expval-base quantities; 3. Support for ``qml.state()`` and ``qml.stateprep()``; 4. Support for all gates support via Matrix Product Operator (MPO).
   [(#909)](https://github.com/PennyLaneAI/pennylane-lightning/pull/909)
 

README.rst

@@ -224,7 +224,7 @@ To install Lightning-GPU from the package sources using the direct SDK path, Lig
     PL_BACKEND="lightning_qubit" python scripts/configure_pyproject_toml.py
     SKIP_COMPILATION=True pip install -e . --config-settings editable_mode=compat -vv
 
-*If cuQuantum SDK is not installed in Python environment ``site-packages`` directory*, a ``CUQUANTUM_SDK`` environment variable has to be set with:
+``CUQUANTUM_SDK`` environment variable set is optional for most cases. *If cuQuantum SDK is not installed in Python environment ``site-packages`` directory*, it has to be set with:
 .. code-block:: bash
 
     export CUQUANTUM_SDK=$(python -c "import site; print( f'{site.getsitepackages()[0]}/cuquantum')")
@@ -395,7 +395,7 @@ Lightning-Qubit should be installed before Lightning-Tensor (compilation is not
     PL_BACKEND="lightning_qubit" python scripts/configure_pyproject_toml.py
     SKIP_COMPILATION=True pip install -e . --config-settings editable_mode=compat
 
-*If cuQuantum SDK is not installed in Python environment ``site-packages`` directory*, a ``CUQUANTUM_SDK`` environment variable has to be set with:
+``CUQUANTUM_SDK`` environment variable set is optional for most cases. *If cuQuantum SDK is not installed in Python environment ``site-packages`` directory*, it has to be set with:
 .. code-block:: bash
 
     export CUQUANTUM_SDK=$(python -c "import site; print( f'{site.getsitepackages()[0]}/cuquantum')")