Per #2300, add Python package disclaimer for the METplus components

docs/Contributors_Guide/coding_standards.rst

@@ -4,10 +4,30 @@
 Coding Standards
 ****************
 
+Guidelines
+==========
+
 * Python code style outlined in `PEP8 <https://pep8.org>`_
 * `Doxygen <http://www.doxygen.nl/>`_, `Python
   docstrings <https://www.python.org/dev/peps/pep-0257/>`_, and
   `Sphinx <http://www.sphinx-doc.org/en/master/>`_ for documentation
 * **NOTE: Please do not use f-strings in the run_metplus.py file so that the Python version check can notify the user of the incorrect version. Using Python 3.5 or earlier will output the SyntaxError from the f-string instead of the useful error message.**
 
 Python code analysis tools like **pylint** can be used to check for errors and violations of PEP8 standards.
+
+Python Package Disclaimer
+=========================
+
+Any external Python packages used in the METplus components are defined in the
+requirements.txt file and, if applicable, nco_requirements.txt file in the top
+level of the code repositories. It is important that the METplus components only
+require Python packages that are allowed on operational high performance
+computers (HPCs). The process of approval for some HPCs can take months and
+some packages have been denied.
+
+Proceed with caution and request approval before starting development with a
+new Python package. Some general guidelines to consider when choosing new
+potential Python packages are:
+
+  * The package would ideally have a version number of 1 or greater.
+  * Ensure that the package is regularly being maintained.