debian: Add libosmoctrl-doc sub-package

This fixes the debian package builds for libosmocore.git

Change-Id: I454e3c0175ab5a89e8925e036a3644299367df0f
diff --git a/debian/libosmoctrl-doc.doc-base b/debian/libosmoctrl-doc.doc-base
new file mode 100644
index 0000000..173d157
--- /dev/null
+++ b/debian/libosmoctrl-doc.doc-base
@@ -0,0 +1,7 @@
+Document: libosmoctrl-doc
+Title: Documentation for the libosmoctrl library
+Section: Programming
+
+Format: HTML
+Index: /usr/share/doc/libosmocore/ctrl/html/index.html
+Files: /usr/share/doc/libosmocore/ctrl/html/*.html