add flintshire_gov_uk

doc/source/flintshire_gov_uk.md

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+# Flintshire, United Kingdom
+
+Support for schedules provided by [Flintshire, United Kingdom](https://flintshire.gov.uk/), serving Flintshire, UK.
+
+## Configuration via configuration.yaml
+
+```yaml
+waste_collection_schedule:
+    sources:
+    - name: flintshire_gov_uk
+      args:
+        uprn: "UPRN"
+        
+```
+
+### Configuration Variables
+
+**uprn**  
+*(String | Integer) (required)*
+
+
+## Example
+
+```yaml
+waste_collection_schedule:
+    sources:
+    - name: flintshire_gov_uk
+      args:
+        uprn: "100100211557"
+        
+```
+
+## How to get the source argument
+
+An easy way to discover your Unique Property Reference Number (UPRN) is by going to <https://www.findmyaddress.co.uk/> and entering in your address details.
+
+Alternatively you can inspect your browsers traffic in the network section of the developer tools (F12 or right click -> inspect element) and look for a request to `https://digital.flintshire.gov.uk/FCC_BinDay/Home/Details2/200001744973` where `200001744973` is the UPRN.