DOC: Reword description about patching in preview mode (#2491)

* reword description about patching in preview

* corrections about patching non-sklearn classes

* include necessary file

Author: david-cortes-intel

doc/sources/non-scikit-algorithms.rst

@@ -17,7 +17,11 @@
 Non-Scikit-Learn Algorithms
 ===========================
 Algorithms not presented in the original scikit-learn are described here. All algorithms are
-available for both CPU and GPU (including distributed mode)
+available for both CPU and GPU (including distributed mode).
+
+.. Note::
+    If using :ref:`patching <patching>`, these classes can be imported either from module ``sklearn``
+    or from module ``sklearnex``.
 
 .. autoclass:: sklearnex.basic_statistics.BasicStatistics
     :members:

doc/sources/preview.rst

@@ -12,6 +12,7 @@
 .. See the License for the specific language governing permissions and
 .. limitations under the License.
 
+.. include:: substitutions.rst
 .. _preview:
 
 #####################
@@ -29,8 +30,8 @@ for being enabled by default for all users:
 This type of functionality is available under **preview mode** of |sklearnex| and located in
 the corresponding module (`sklearnex.preview`).
 
-Preview functionality *may* or *may not* participate in patching of Scikit-learn.
-For example, a preview estimator may be a replacement for a stock one or a completely new one.
+Functionalities under preview will be made available after patching when preview mode is enabled,
+but note that some might be :ref:`extension estimators <extension_estimators>` without analogs in |sklearn|.
 
 To enable preview functionality, you need to set the `SKLEARNEX_PREVIEW` environment variable
 to non-empty value before patching of Scikit-learn.