Add note to Sphinx from requirements.txt in editing_these_docs.rst

Installing from the requirements.txt file will make sure that the
the version number constraints will be applied during installation
of Sphinx anbd its dependencies.

Signed-off-by: Bob Yantosca <yantosca@seas.harvard.edu>

docs/source/reference/editing_these_docs.rst

@@ -5,8 +5,8 @@
 Editing this User Guide
 #######################
 
-This user guide is generated with `Sphinx <https://www.sphinx-doc.org/>`_. 
-Sphinx is an open-source Python project designed to make writing software documentation easier. 
+This user guide is generated with `Sphinx <https://www.sphinx-doc.org/>`_.
+Sphinx is an open-source Python project designed to make writing software documentation easier.
 The documentation is written in a reStructuredText (it's similar to markdown), which Sphinx extends for software documentation.
 The source for the documentation is the :file:`docs/source` directory in top-level of the source code.
 
@@ -15,14 +15,17 @@ Quick start
 ===========
 
 To build this user guide on your local machine, you need to install Sphinx. Sphinx is a Python 3 package and
-it is available via :program:`pip`. This user guide uses the Read The Docs theme, so you will also need to 
+it is available via :program:`pip`. This user guide uses the Read The Docs theme, so you will also need to
 install :literal:`sphinx-rtd-theme`. It also uses the `sphinxcontrib-bibtex <https://pypi.org/project/sphinxcontrib-bibtex/>`_
 and `recommonmark <https://recommonmark.readthedocs.io/>`_ extensions, which you'll need to install.
 
 .. code-block:: console
 
-   $ pip install sphinx sphinx-rtd-theme sphinxcontrib-bibtex recommonmark
+   $ cd $KPP_HOME/docs
+   $ pip install -r requirements.txt
 
+Installing with :file:`requirements.txt` will make sure that the
+proper versions of Sphinx and its dependencies will be installed.
 
 To build this user guide locally, navigate to the :file:`docs/` directory and make the :literal:`html` target.
 
@@ -34,7 +37,7 @@ To build this user guide locally, navigate to the :file:`docs/` directory and ma
 
 This will build the user guide in :file:`docs/build/html`, and you can
 open :file:`index.html` in your  web-browser. The source files for the
-user guide are found in :file:`docs/source`.   
+user guide are found in :file:`docs/source`.
 
 .. note::
 
@@ -50,27 +53,27 @@ can be easily miswritten. Two important things you should know right away are:
 * Indents are 3-spaces
 * "Things" are separated by 1 blank line. For example, a list or
   code-block following a paragraph should be separated from the
-  paragraph by 1 blank line. 
+  paragraph by 1 blank line.
 
 You should keep these in mind when you're first getting
 started. Dedicating an hour to learning reST will save you time in the
 long-run.  Below are some good resources for learning reST.
 
 * `reStructuredText primer
   <https://www.sphinx-doc.org/en/master/usage/restructuredtext/basics.html>`_:
-  (single best resource; however, it's better read than skimmed) 
+  (single best resource; however, it's better read than skimmed)
 * Official `reStructuredText reference
   <https://docutils.sourceforge.io/docs/user/rst/quickref.html>`_
-  (there is *a lot* of information here) 
+  (there is *a lot* of information here)
 * `Presentation by Eric Holscher
   <https://www.youtube.com/watch?v=eWNiwMwMcr4>`_ (co-founder of Read
   The Docs) at DjangoCon US 2015 (the entire presentation is good, but
-  reST is described from 9:03 to 21:04) 
+  reST is described from 9:03 to 21:04)
 * `YouTube tutorial by Audrey Tavares's
-  <https://www.youtube.com/watch?v=DSIuLnoKLd8>`_ 
+  <https://www.youtube.com/watch?v=DSIuLnoKLd8>`_
 
 A good starting point would be Eric Holscher's presentations followed
-by the reStructuredText primer. 
+by the reStructuredText primer.
 
 ================
 Style guidelines
@@ -96,19 +99,19 @@ For **titles and headers**:
 the :literal:`:file:` role.
 
 **Program names** (e.g. :program:`cmake`) occuring in the text should
-use the :literal:`:program:` role. 
+use the :literal:`:program:` role.
 
 **OS-level commands** (e.g. :command:`rm`) occuring in the text should
-use the :literal:`:command:` role. 
+use the :literal:`:command:` role.
 
 **Environment variables** occuring in the text should use the
-:literal:`:envvar:` role. 
+:literal:`:envvar:` role.
 
 **Inline code** or code variables occuring in the text should use the
-:literal:`:code:` role. 
+:literal:`:code:` role.
 
 **Code snippets** should use :literal:`.. code-block:: <language>`
-directive like so 
+directive like so
 
 .. code-block:: none
 
@@ -117,7 +120,7 @@ directive like so
       import gcpy
       print("hello world")
 
-The language can be "none" to omit syntax highlighting. 
+The language can be "none" to omit syntax highlighting.
 
 For command line instructions, the "console" language should be
 used. The :literal:`$` should be used to denote the console's
@@ -126,4 +129,4 @@ instructions, a prompt like :literal:`gcuser:~/path1/path2$` should be
 used.
 
 **Inline literals** (e.g. the :literal:`$` above) should use the
-:literal:`:literal:` role. 
+:literal:`:literal:` role.