Add documentation for new Start.ca sensor (#4658)

New sensor for ISP usage data for Start.ca

source/_components/sensor.startca.markdown

@@ -0,0 +1,84 @@
+---
+layout: page
+title: "Start.ca"
+description: "Instructions on how to integrate Start.ca data usage within Home Assistant."
+date: 2018-02-12 00:00
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: startca.png
+ha_category: Sensor
+ha_release: 0.64
+ha_iot_class: "Cloud Polling"
+---
+
+Integrate your [Start.ca](https://www.start.ca/) account information into Home Assistant.
+
+You can get your API key from:
+
+[Start.ca Usage API](https://www.start.ca/support/usage/api)
+
+To use your Start.ca sensor in your installation, add the following to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+sensor:
+  - platform: startca
+    api_key: API_KEY
+    total_bandwidth: 400
+    monitored_variables:
+      - usage
+      - usage_gb
+      - limit
+      - used_download
+      - used_upload
+      - used_total
+      - grace_download
+      - grace_upload
+      - grace_total
+      - total_download
+      - total_upload
+      - used_remaining
+```
+
+{% configuration %}
+api_key:
+  description: The Start.ca API key to access the service.
+  required: true
+  type: string
+total_bandwidth:
+  description: Your bandwidth limit in gigabytes. Set to `0` for unlimited plans without a cap.
+  required: true
+  type: string
+monitored_conditions:
+  description: Conditions to display in the frontend.
+  required: true
+  type: list
+  keys:
+    usage:
+      description: Bandwidth usage (percentage).
+    usage_gb:
+      description: Bandwidth usage (gigabytes).
+    limit:
+      description: Monthly bandwidth limit (gigabytes).
+    used_download:
+      description: Bandwidth used by download outside the grace period (gigabytes).
+    used_upload:
+      description: Bandwidth used by upload outside the grace period (gigabytes).
+    used_total:
+      description: Total bandwidth (download and upload sum calculation) used outside the grace period (gigabytes).
+    grace_download:
+      description: Bandwidth used by download during the grace period (gigabytes).
+    grace_upload:
+      description: Bandwidth used by upload during the grace period (gigabytes).
+    grace_total:
+      description: Total bandwidth (download and upload sum calculation) used during the unlimited period (gigabytes).
+    total_download:
+      description: Total bandwidth download (Grace + Used) (gigabytes).
+    total_download:
+      description: Total bandwidth upload (Grace + Used) (gigabytes).
+    used_remaining:
+      description: Remaining bandwidth calucated from used and supplied total bandwidth (gigabytes).
+{% endconfiguration %}
+