Need conda-forge channel in installation instruction

This resolves gh-1749, where absense of conda-forge among channels
caused installation of a very old version of dpctl

Author: oleksandr-pavlyk

docs/doc_sources/beginners_guides/installation.rst

@@ -30,14 +30,14 @@ indicated by ``--channel`` option:
 .. code-block:: bash
     :caption: Getting latest released version of ``dpctl`` using conda
 
-    conda create --name dpctl_env --channel https://software.repos.intel.com/python/conda/ dpctl
+    conda create --name dpctl_env --channel https://software.repos.intel.com/python/conda/ --channel conda-forge dpctl
 
 Development builds of ``dpctl`` can be accessed from the ``dppy/label/dev`` channel:
 
 .. code-block:: bash
     :caption: Getting latest development version
 
-    conda create -n dpctl_nightly -c dppy/label/dev -c https://software.repos.intel.com/python/conda/ dpctl
+    conda create -n dpctl_nightly -c dppy/label/dev -c https://software.repos.intel.com/python/conda/ -c conda-forge dpctl
 
 .. note::
     If :py:mod:`dpctl` is not available for the Python version of interest,