Add UK government API catalogue

This isn't an API but rather the site where they are collated by the UK
government.

I've added the data.gov.uk site as a separate entry for clarity (because
of the number of similar sites from other countries). This site is also
linked to from the API catalogue site.

README.md

@@ -530,8 +530,10 @@ API | Description | Auth | HTTPS | CORS |
 | [Open Government, Romania](http://data.gov.ro/) | Romania Government Open Data | No | No | Unknown |
 | [Open Government, Taiwan](https://data.gov.tw/) | Taiwan Government Open Data | No | Yes | Unknown |
 | [Open Government, Thailand](https://data.go.th/) | Thailand Government Open Data | `apiKey` | Yes | Unknown |
+| [Open Government, UK](https://data.gov.uk/) | UK Government Open Data | No | Yes | Unknown |
 | [Open Government, USA](https://www.data.gov/) | United States Government Open Data | No | Yes | Unknown |
 | [Represent by Open North](https://represent.opennorth.ca/) | Find Canadian Government Representatives | No | Yes | Unknown |
+| [UK government API catalogue](https://alphagov.github.io/api-catalogue) | APIs from UK government organisations | No | Yes | Unknown |
 | [USAspending.gov](https://api.usaspending.gov/) | US federal spending data | No | Yes | Unknown |
 
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