Fill out experiments section a bit (#32)

* Fill out experiments section a bit

Still a WIP but adds a few lines about different experimentation platforms and links to other docs

* Update experiments section w PR suggestions

tools/experiments.md

@@ -5,3 +5,30 @@ The work is being tracked in
 [this bug](https://bugzilla.mozilla.org/show_bug.cgi?id=1341812).
 
 # Guide to our Experimental Tools
+
+## Shield
+* Shield is an addon-based experimentation platform with fine-tuned enrollment criteria. The system add-on landed in FF 53.
+* For the moment, it sends back data in its own `shield` type ping, so there's lots of flexibility in data you can collect.
+* Uses the Normandy server to serve out study “recipes” (?)
+* Annotates the main ping in the environment/experiments block
+* The shield system is itself a system add-on, so rolling out changes to the entire system does not require riding release trains
+* Strategy and Insights (strategyandinsights@mozilla.com) team are product owners and shepherd the study development and release process along
+* Opt-out experiments should be available soon?
+* Further reading:
+    * https://wiki.mozilla.org/Firefox/SHIELD
+    * https://wiki.mozilla.org/Firefox/Shield/Shield_Studies
+    * https://mozilla.github.io/shield-studies-docs/study-process/
+    * When should you use SHIELD over other options?
+ 
+## Preference Flipping experiments
+Uses Normandy, requires NO additional addon as long as a preference rides the release train
+ 
+## Heartbeat
+Survey mechanism, also run via Normandy
+ 
+## Telemetry Experiments
+Pre-release only
+https://gecko.readthedocs.io/en/latest/browser/experiments/experiments/index.html
+ 
+## Funnelcake
+Custom builds of Firefox that are served to some percentage of the direct download population