Doxygen: Base/Parameter.h description

Adding a cursory description for `Parameter.h` + typo fix for it's companion .cpp file. 

.

src/Base/Parameter.cpp

@@ -81,7 +81,7 @@ using namespace Base;
 
 //**************************************************************************
 //**************************************************************************
-// privat classes declaration:
+// private classes declaration:
 // - DOMTreeErrorReporter
 // - StrX
 // - DOMPrintFilter

src/Base/Parameter.h

@@ -22,6 +22,13 @@
  *   Juergen Riegel 2002                                                   *
  ***************************************************************************/
 
+ /** 
+ * \file Parameter.h
+ * \brief The classes defined here are used to interface with the XML-based
+ * FreeCAD config files: user.cfg and system.cfg files. It can parse, get,
+ * and store the parameters/configurations for the user's preferences.
+ * 3rd party Xerces-C++ XML parser is used to parse and write the XML.
+ */
 
 #ifndef BASE__PARAMETER_H
 #define BASE__PARAMETER_H