Added isis class documentation guidelines

docs/how-to-guides/isis-developer-guides/isis-class-documentation.md

@@ -0,0 +1,30 @@
+# ISIS Class Documentation with Doxygen
+
+A new ISIS3 class needs to have the following Doxygen tags filled out just above the class declaration, as in this example below:
+
+```/**
+    * @brief Add map templates to a project
+    * Asks the user for a map template and copies it into the project.
+    *
+    * @author 2018-07-05 Summer Stapleton
+    * @internal
+    *    @history 2018-07-05 Summer Stapleton - Created ImportMapTemplateWorkOrder
+    *                        class
+    *
+    */
+    class ImportMapTemplateWorkOrder : public WorkOrder {....
+```
+Sometimes, classes are declared inside the header files for other classes.  This happens a lot in the $ISISROOT/src/qisis/objs directory where internal XmlHandler classes are defined to handle object serialization.
+These classes need to be documented as well (as in this example from the ImageList header file):
+
+```/**
+       * This class is used to read an images.xml file into an image list
+       *
+       * @author 2012-07-01 Steven Lambright
+       *
+       * @internal
+       */
+      class XmlHandler : public XmlStackedHandler {
+```
+
+All dates need to be filled out the way they are in the examples above (YYYY-MM-DD).  Sometimes you will see dates in this format:  2012-??-???? or  ????-??-??.  Do not do this.  Also, do not put any dashes or other symbols between the date and the name of the programmer.

mkdocs.yml

@@ -72,6 +72,7 @@ nav:
       - Class Requirements For Using Doxygen Tags:    how-to-guides/isis-developer-guides/class-requirements-for-using-doxygen-tags.md
       - Developing ISIS3 with cmake:                  how-to-guides/isis-developer-guides/developing-isis3-with-cmake.md
       - ISIS Development on the Mac M1 ARM System:    how-to-guides/isis-developer-guides/developing-mac-m1-arm-systems.md
+      - ISIS Class Documentation:                     how-to-guides/isis-developer-guides/isis-class-documentation.md
     - ALE Developer Guides:
       - Creating Ale Drivers: how-to-guides/ale-developer-guides/creating-ale-drivers.md
   - Concepts: