Added Gearbest Sensor (#3973)

* Added Gearbest Sensor

* Updated gearbest markdown to reflect latest changes

* 🚑 Adds missing Gearbest logo

* 🏁 Updated HA release version

* ✏️ Corrected some minor language issues

* 🔨 Rewritten configuration options to use configuration tags

* Minor updates

source/_components/sensor.gearbest.markdown

@@ -0,0 +1,72 @@
+---
+layout: page
+title: "Gearbest"
+description: "Instructions on how to integrate a Gearbest sensor into Home Assistant."
+date: 2017-11-13 09:08
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: gearbest.png
+ha_category: Sensor
+ha_iot_class: "Cloud Polling"
+ha_release: "0.60"
+---
+
+
+The `gearbest` sensor will track the price of a product from [Gearbest](https://www.gearbest.com). This information can be used in, e.g., automations to notify you when a price drops. The update interval for every item is currently set to 2 hours.
+
+To enable this sensor, add the following lines to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+sensor:
+  - platform: gearbest
+    currency: EUR
+    items:
+      - url: https://www.gearbest.com/....
+```
+
+{% configuration %}
+currency:
+  description: "The currency in which the products should be tracked. Currently supported: USD, EUR, GBP, AUD, CAD, CHF, HKD, CNY, NZD, JPY, RUB, BRL, CLP, NOK, DKK, SEK, KRW, ILS, COP, MXN, PEN, THB, IDR, UAH, PLN, INR, BGN, HUF, RON, TRY, CZK, HRK, MAD, AED, SAR, ZAR, SGD, MYR, TWD, RSD, NGN - if the currency could not be found in the conversion rate list, USD will be used as default. Either an ID or an URL must be present."
+  required: true
+  type: string
+items:
+  description: List of products that should be tracked.
+  required: true
+  type: map
+  keys:
+    id:
+      description: The ID of the product.
+      required: false
+      type: int
+    url:
+      description: The URL of the product.
+      required: false
+      type: string
+    name:
+      description: The name of the item. If not set, it is parsed from the website.
+      required: false
+      type: string
+    currency:
+      description: Overwrite the currency for the current item.
+      required: false
+      type: string
+{% endconfiguration %}
+
+### {% linkable_title Extended example %}
+
+```yaml
+# Example configuration.yaml entry
+sensor:
+  - platform: gearbest
+    currency: EUR
+    items:
+      - url: https://www.gearbest.com/3d-printers-3d-printer-kits/pp_779174.html?wid=21
+        name: Creality CR-10 upgraded
+        currency: USD
+      - id: 779174
+        name: Creality CR-10 upgraded #2
+        currency: EUR
+```