DOC: list conda install cmd with pinned pyqt under warning section

Since pyqt=5 is valid install option, just designer won't work with pydm
widgets.
Explicity list the cmd for pyqt=5.12.3, to avoid any confusion on how
to pin, and maybe to catch anyone's eyes just looking for install cmds.

docs/source/installation.rst

@@ -17,16 +17,18 @@ Installing PyDM and Prerequisites with Anaconda
 After installing Anaconda (see https://www.anaconda.com/download/), create a new
 environment for PyDM::
   
-  $ conda create -n pydm-environment python=3.8 pyqt=5.12.3 pip numpy scipy six psutil pyqtgraph pydm -c conda-forge
+  $ conda create -n pydm-environment python=3.8 pyqt=5 pip numpy scipy six psutil pyqtgraph pydm -c conda-forge
   $ source activate pydm-environment
 
 .. warning::
     There is currently no PyQt 5.15+ build available on conda or PyPI that has
-    designer support for python plugins.
+    designer support for python plugins. PyDM widgets will not load in these designer versions.
 
-    In order to use PyDM widgets in designer, we make sure to pin the PyQt version to 5.12.3 or lower
+    In order to use PyDM widgets in designer, please make sure to pin the PyQt version to 5.12.3 or lower
     until this is resolved.
 
+    $ conda create -n pydm-environment python=3.8 pyqt=5.12.3 pip numpy scipy six psutil pyqtgraph pydm -c conda-forge
+
 Once you've installed and activated the environment, you should be able to run 'pydm' to launch PyDM, or run 'designer' to launch Qt Designer.  If you are on Windows, run these commands from the Anaconda Prompt.
 
 On MacOS, launching Qt Designer is a little more annoying: