Add module docs for RTD generation (#6397)

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

**Context:** Adds module-level documentation for `qml.labs` 

**Description of the Change:**

**Benefits:**

**Possible Drawbacks:**

**Related GitHub Issues:**

---------

Co-authored-by: Josh Izaac <josh146@gmail.com>

doc/code/qml_labs.rst

@@ -0,0 +1,7 @@
+qml.labs
+================
+
+.. currentmodule:: pennylane.labs
+
+.. automodule:: pennylane.labs
+

doc/index.rst

@@ -201,6 +201,7 @@ PennyLane is **free** and **open source**, released under the Apache License, Ve
    code/qml_fourier
    code/qml_gradients
    code/qml_kernels
+   code/qml_labs
    code/qml_logging
    code/qml_math
    code/qml_noise

doc/releases/changelog-dev.md

@@ -45,6 +45,9 @@
 
 <h3>Improvements 🛠</h3>
 
+* RTD support for `qml.labs` added to API.
+  [(#6397)](https://github.com/PennyLaneAI/pennylane/pull/6397)
+
 * Module-level sandboxing added to `qml.labs` via pre-commit hooks.
   [(#6369)](https://github.com/PennyLaneAI/pennylane/pull/6369)
 

pennylane/labs/__init__.py

@@ -11,8 +11,26 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-""":code:`pennylane/labs/` module contains experimental features enabling
-advanced quantum computing research."""
+r"""
+.. currentmodule:: pennylane
 
+This module module contains experimental features enabling
+advanced quantum computing research.
+
+.. warning::
+
+    This module is experimental. Frequent changes will occur,
+    with no guarantees of stability or backwards compatibility.
+
+.. currentmodule:: pennylane.labs
+
+Modules
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. autosummary::
+    :toctree: api
+
+
+"""
 
 __all__ = []