doc files copyright (#3843)

* doc files copyright

* fix indentation

docs/doxygen/ngraph_cpp_api.config

@@ -1,3 +1,18 @@
+# Doxyfile 1.8.18
+
+# This file describes the settings to be used by the documentation system
+# doxygen (www.doxygen.org) for a project.
+#
+# All text after a double hash (##) is considered a comment and is placed in
+# front of the TAG it is preceding.
+#
+# All text after a single hash (#) is considered a comment and will be ignored.
+# The format is:
+# TAG = value [value, ...]
+# For lists, items can also be appended using:
+# TAG += value [value, ...]
+# Values that contain spaces should be placed between quotes (\" \").
+
 @INCLUDE = "@IE_CONFIG_BUILD@"
 
 EXCLUDE_SYMBOLS        =