update apidocs ui section to Umbraco 13

src/Umbraco.Web.UI.Docs/.nvmrc

@@ -0,0 +1 @@
+10.15

src/Umbraco.Web.UI.Docs/README.md

@@ -1,12 +1,14 @@
 # Umbraco Backoffice UI API Documentation
 
-This project builds the documentation for the UI of the Umbraco backoffice, it is published on Our Umbraco in the "Reference" section of the documentation.
+This project builds the documentation for the UI of the Umbraco backoffice, it is published on the Umbraco Docs in the "Reference" section of the documentation.
+
+All versions can be accessed through the https://apidocs.umbraco.com/vXX/ui/ url where XX is the major version number of Umbraco.
 
 In order to build the documentation, please follow the following two steps:
 
 ```
 npm ci
-npx gulp docs
+npm start
 ```
 
 After this, you should have an `api` directory which contains index.html. 

src/Umbraco.Web.UI.Docs/gulpfile.js

@@ -18,7 +18,7 @@ gulp.task('docs', [], function (cb) {
     var options = {
         html5Mode: false,
         startPage: '/api',
-        title: "Umbraco 12 Backoffice UI API Documentation",
+        title: "Umbraco 13 Backoffice UI API Documentation",
         dest: './api',
         styles: ['./umb-docs.css'],
         image: "https://our.umbraco.com/assets/images/logo.svg"