Update installation instructions for LT and LGPU (#957)

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------------------------------------------------------------------------------------------------------------

**Context:**

[sc-76616]

**Description of the Change:**

**Benefits:**

**Possible Drawbacks:**

**Related GitHub Issues:**

---------

Co-authored-by: ringo-but-quantum <[email protected]>
Co-authored-by: Joseph Lee <[email protected]>

.github/CHANGELOG.md

@@ -46,6 +46,9 @@
 
 ### Improvements
 
+* Update `README.rst` installation instructions for `lightning.gpu` and `lightning.tensor`.
+  [(#957)](https://github.com/PennyLaneAI/pennylane-lightning/pull/957)
+
 * Optimize `GlobalPhase` and `C(GlobalPhase)` gate implementation in `lightning.gpu`.
   [(#946)](https://github.com/PennyLaneAI/pennylane-lightning/pull/946)
 

README.rst

@@ -220,10 +220,11 @@ To install Lightning-GPU from the package sources using the direct SDK path, Lig
     git clone https://github.com/PennyLaneAI/pennylane-lightning.git
     cd pennylane-lightning
     pip install -r requirements.txt
+    pip install custatevec-cu12
     PL_BACKEND="lightning_qubit" python scripts/configure_pyproject_toml.py
     SKIP_COMPILATION=True pip install -e . --config-settings editable_mode=compat -vv
 
-Then the `custatevec-cu12 <https://pypi.org/project/cuquantum-cu12/>`_ library can be installed and set a ``CUQUANTUM_SDK`` environment variable.
+Then a ``CUQUANTUM_SDK`` environment variable can be set:
 
 .. code-block:: bash
 
@@ -391,10 +392,11 @@ Lightning-Qubit should be installed before Lightning-Tensor (compilation is not
     git clone https://github.com/PennyLaneAI/pennylane-lightning.git
     cd pennylane-lightning
     pip install -r requirements.txt
+    pip install cutensornet-cu12
     PL_BACKEND="lightning_qubit" python scripts/configure_pyproject_toml.py
     SKIP_COMPILATION=True pip install -e . --config-settings editable_mode=compat
 
-Then the `cutensornet <https://docs.nvidia.com/cuda/cuquantum/latest/cutensornet/index.html>`_ library can be installed and set a ``CUQUANTUM_SDK`` environment variable.
+Then a ``CUQUANTUM_SDK`` environment variable can be set:
 
 .. code-block:: bash
 

pennylane_lightning/core/_version.py

@@ -16,4 +16,4 @@
    Version number (major.minor.patch[-label])
 """
 
-__version__ = "0.39.0-dev48"
+__version__ = "0.39.0-dev49"