Create configuring_prometheus.md

Add documentation on how to export metrics to prometheus.

templates/docs/configuring_prometheus.md

@@ -0,0 +1,26 @@
+# Configuring Prometheus
+
+Healthchecks.io supports exporting metrics and check statuses to [Prometheus](https://prometheus.io/), for use with [Grafana](https://grafana.com/).  
+
+You can generate the metrics export endpoint by going to your project settings (last tab up top) and clicking "Create API Keys". You will then see the link to the prometheus endpoint, which looks like this:
+
+```
+https://healthchecks.io/projects/45sd78-eeee-dddd-8888-b25a9887ecfd/metrics/NXyGzks4s8xcF1J-wzoaioyoqXIANGD0
+```
+
+## Update the prometheus.yml
+
+You can take that link and add it to the prometheus config:
+
+```yaml
+  - job_name: "healthchecks"
+    scrape_interval: 60s
+    scheme: https
+    metrics_path: /projects/45sd78-eeee-dddd-8888-b25a9887ecfd/metrics/NXyGzks4s8xcF1J-wzoaioyoqXIANGD0
+    static_configs:
+      - targets: ["healthchecks.io"]
+```
+
+Notice how we split up the URL and paste in the scheme, domain, and path separately. 
+
+Reload promethus and your changes should be live, coming in under the `hc_` prefix.

templates/front/base_docs.html

@@ -32,6 +32,7 @@
         {% include "front/docs_nav_item.html" with slug="measuring_script_run_time" title="Measuring script run time" %}
         {% include "front/docs_nav_item.html" with slug="attaching_logs" title="Attaching logs" %}
         {% include "front/docs_nav_item.html" with slug="cloning_checks" title="Cloning Checks" %}
+        {% include "front/docs_nav_item.html" with slug="configuring_prometheus" title="Configuring Prometheus" %}
 
         <li class="nav-header">Developer Tools</li>
         {% include "front/docs_nav_item.html" with slug="api" title="Management API" %}
@@ -47,4 +48,4 @@
         {% endblock %}
     </div>
 </div>
-{% endblock %}
+{% endblock %}