doxygen: also generate documentation for libosmo{sim,usb}

We do have API documentation for all libraries, excepte these two.

Change-Id: I2ec5803bc219b9ceaf0d52d41a03ab78f580e689
diff --git a/debian/libosmousb-doc.doc-base b/debian/libosmousb-doc.doc-base
new file mode 100644
index 0000000..6121918
--- /dev/null
+++ b/debian/libosmousb-doc.doc-base
@@ -0,0 +1,7 @@
+Document: libosmousb-doc
+Title: Documentation for the libosmousb library
+Section: Programming
+
+Format: HTML
+Index: /usr/share/doc/libosmocore/usb/html/index.html
+Files: /usr/share/doc/libosmocore/usb/html/*.html