[tracker-miners] Add a stub HACKING.md file.

[Sam Thursfield <sthursfield src gnome org>]

commit 85d6b70cfd6b432532e698733ec018a9b3653c83
Author: Sam Thursfield <sam afuera me uk>
Date:   Sun Sep 29 17:56:33 2019 +0200

    Add a stub HACKING.md file.
    
    This just links to tracker.git.

 HACKING.md | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/HACKING.md b/HACKING.md
new file mode 100644
index 000000000..6f7edbe7e
--- /dev/null
+++ b/HACKING.md
@@ -0,0 +1,2 @@
+Please see the file HACKING.md in Tracker core:
+https://gitlab.gnome.org/GNOME/tracker/blob/master/HACKING.md