Add command to build specific files in Building the manual with Sphinx (#5828)

community/contributing/building_the_manual.rst

@@ -82,6 +82,12 @@ program manually:
 
    sphinx-build -b html ./ _build
 
+You can also specify a list of files to build, which can greatly speed up compilation:
+
+.. code:: sh
+
+  sphinx-build -b html ./ _build classes/class_node.rst classes/class_resource.rst
+
 Building with Sphinx and virtualenv
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