Improve guidance for Makefiles added for mkdocs tool

Author: mpilgrem

CONTRIBUTING.md

@@ -245,7 +245,7 @@ Command `mkdocs build` to build the documentation.
     the MSYS2 environment:
 
     ~~~text
-    stack exec -- pacman --sync python libxml2-devel libxslt-devel
+    stack exec -- pacman --sync python make libxml2-devel libxslt-devel
     ~~~
 
     !!! note

Makefile

@@ -1,5 +1,6 @@
-# This file allows users of the 'make' tool to automate the use of the 'mkdocs'
-# tool to preview or build Stack's online documentation.
+# With the other prerequisites, this file allows users of the 'make' tool to
+# automate the use of the 'mkdocs' tool to preview or build Stack's online
+# documentation. See CONTRIBUTING.md for more information.
 
 # Preview Stack's online documentation with `make docs-serve`:
 .PHONY: docs-serve

doc/Makefile

@@ -1,6 +1,7 @@
-# This file allows users of the 'make' tool to automate the use of the 'mkdocs'
-# tool to preview or build Stack's online documentation. See the file 'Makefile'
-# in Stack's project directory for more information.
+# With the necessary prerequisites, this file allows users of the 'make' tool to
+# automate the use of the 'mkdocs' tool to preview or build Stack's online
+# documentation. See CONTRIBUTING.md and the file 'Makefile' in Stack's project
+# directory for more information.
 
 PYTHON_VIRTUALENV:=.python-doc-virtualenv
 MK_DOCS_CMD:=$(PYTHON_VIRTUALENV)/bin/mkdocs