[tracker/sam/debug: 3/3] HACKING.md: Document the available debug options

[Sam Thursfield <sthursfield src gnome org>]

commit cc62f84824287c54fb88f0e0fd62f28b18bace6e
Author: Sam Thursfield <sam afuera me uk>
Date:   Mon Apr 20 02:44:51 2020 +0200

    HACKING.md: Document the available debug options

 HACKING.md | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/HACKING.md b/HACKING.md
index 61a40e192..985c0872c 100644
--- a/HACKING.md
+++ b/HACKING.md
@@ -37,6 +37,12 @@ The following environment variables control logging from Tracker daemons:
   * `TRACKER_DEBUG`: takes a comma-separated list of keywords to enable
     extra debugging output. Use the keyword 'help' for a list of keywords.
 
+    Options include:
+
+        - sql-indexes
+        - sql-statements
+        - miner-fs-events
+
 You can set these variables when using `tracker-sandbox`, and when running the
 Tracker test suite. Note that Meson will not print log output from tests by
 default, use `meson test --verbose` or `meson test --print-errorlogs` to