Add a Doxyfile for update_engine codebase am: 8b113b21b8

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/1421968

Change-Id: Ida5549b52c29abc2a7305c32dccc955d331937c2
diff --git a/Doxyfile b/Doxyfile
new file mode 100644
index 0000000..db31f86
--- /dev/null
+++ b/Doxyfile
@@ -0,0 +1,9 @@
+CLANG_DATABASE_PATH=../../
+HAVE_DOT=YES
+CALL_GRAPH=YES
+CALLER_GRAPH=YES
+GENERATE_HTML=YES
+GENERATE_LATEX=NO
+INPUT=.
+RECURSIVE=YES
+