Add StatsD readme (#702)

* Adding draft notes for statsd readme

* Add statsd dashboard json template & image.

docs/rpc_statsd.md

@@ -0,0 +1,143 @@
+# Remote monitoring with StatsD
+
+StatsD allows you to receive and aggregate metrics from a wide range of application and retransmit them to the backend of your choice.
+This enables you to create nice and readable dashboards containing all the information you need on your fuzzer instances.
+No need to write your own statistics parsing system, deploy and maintain it to all your instances, sync with your graph rendering system...
+
+The available metrics are :
+- cycle_done
+- cycles_wo_finds
+- execs_done
+- execs_per_sec
+- paths_total
+- paths_favored
+- paths_found
+- paths_imported
+- max_depth
+- cur_path
+- pending_favs
+- pending_total
+- variable_paths
+- unique_crashes
+- unique_hangs
+- total_crashes
+- slowest_exec_ms
+- edges_found
+- var_byte_count
+- havoc_expansion
+
+Compared to the default integrated UI, these metrics give you the opportunity to visualize trends and fuzzing state over time.
+By doing so, you might be able to see when the fuzzing process has reached a state of no progress, visualize what are the "best strategies"
+(according to your own criteria) for your targets, etc. And doing so without requiring to log into each instance manually.
+
+An example visualisation may look like the following:
+![StatsD Grafana](./visualization/StatsD-grafana.png)
+
+*Notes: The exact same dashboard can be imported with [this JSON template](./statsd/grafana-afl++.json).*
+
+## How to use
+
+To enable the StatsD reporting on your fuzzer instances, you need to set the environment variable `AFL_STATSD=1`.
+
+Setting `AFL_STATSD_TAGS_FLAVOR` to the provider of your choice will assign tags / labels to each metric based on their format.
+The possible values are  `dogstatsd`, `librato`, `signalfx` or `influxdb`.
+For more information on these env vars, check out `docs/env_variables.md`.
+
+The simplest way of using this feature is to use any metric provider and change the host/port of your StatsD daemon,
+with `AFL_STATSD_HOST` and `AFL_STATSD_PORT`, if required (defaults are `localhost` and port `8125`).
+To get started, here are some instruction with free and open source tools.
+The following setup is based on Prometheus, statsd_exporter and Grafana.
+Grafana here is not mandatory, but gives you some nice graphs and features.
+
+Depending on your setup and infrastructure, you may want to run these applications not on your fuzzer instances.
+Only one instance of these 3 application is required for all your fuzzers.
+
+To simplify everything, we will use Docker and docker-compose.
+Make sure you have them both installed. On most common Linux distributions, it's as simple as:
+
+```sh
+curl -fsSL https://get.docker.com -o get-docker.sh
+sh get-docker.sh
+```
+
+Once that's done, we can create the infrastructure.
+Create and move into the directory of your choice. This will store all the configurations files required.
+
+First, create a `docker-compose.yml` containing the following:
+```yml
+version: '3'
+
+networks:
+  statsd-net:
+    driver: bridge
+
+services:
+  prometheus:
+    image: prom/prometheus
+    container_name: prometheus
+    volumes:
+      - ./prometheus.yml:/prometheus.yml
+    command:
+      - '--config.file=/prometheus.yml'
+    restart: unless-stopped
+    ports:
+      - "9090:9090"
+    networks:
+      - statsd-net
+
+  statsd_exporter:
+    image: prom/statsd-exporter
+    container_name: statsd_exporter
+    volumes:
+      - ./statsd_mapping.yml:/statsd_mapping.yml
+    command:
+      - "--statsd.mapping-config=/statsd_mapping.yml"
+    ports:
+      - "9102:9102/tcp"
+      - "8125:9125/udp"
+    networks:
+      - statsd-net
+  
+  grafana:
+    image: grafana/grafana
+    container_name: grafana
+    restart: unless-stopped
+    ports:
+        - "3000:3000"
+    networks:
+      - statsd-net
+```
+
+Then `prometheus.yml`
+```yml
+global:
+  scrape_interval:      15s
+  evaluation_interval:  15s
+
+scrape_configs:
+  - job_name: 'fuzzing_metrics'
+    static_configs:
+      - targets: ['statsd_exporter:9102']
+```
+
+And finally `statsd_mapping.yml`
+```yml 
+mappings:
+- match: "fuzzing.*"
+  name: "fuzzing"
+  labels:
+      type: "$1"
+```
+
+Run `docker-compose up -d`.
+
+Everything should be now setup, you are now able to run your fuzzers with
+
+```
+AFL_STATSD_TAGS_FLAVOR=dogstatsd AFL_STATSD=1 afl-fuzz -M test-fuzzer-1 -i i -o o ./bin/my-application @@
+AFL_STATSD_TAGS_FLAVOR=dogstatsd AFL_STATSD=1 afl-fuzz -S test-fuzzer-2 -i i -o o ./bin/my-application @@
+...
+```
+
+This setup may be modified before use in production environment. Depending on your needs: addind passwords, creating volumes for storage,
+tweaking the metrics gathering to get host metrics (CPU, RAM ...).