[skip ci] added docs for new features

docs/practical-instructions/feature.md

@@ -1,2 +1,22 @@
 # Add a new api endpoint/feature
 
+Most of the api endpoints/features of Vikunja are using the [common web handler](https://code.vikunja.io/web).
+This is a library created by Vikunja in an effort to facilitate the creation of REST endpoints.
+
+This works by abstracting the handling of CRUD-Requests, including rights check.
+
+You can learn more about the web handler on [the project's repo](https://code.vikunja.io/web).
+
+### Helper for pagination
+
+These can be calculated in combination with a helper function, `getLimitFromPageIndex(pageIndex)` which returns
+the `limit` (max-length) and `offset` parameters needed for SQL-Queries.
+
+You can feed this function directly into xorm's `Limit`-Function like so:
+
+```go
+lists := []List{}
+err := x.Limit(getLimitFromPageIndex(pageIndex)).Find(&lists)
+```
+
+// TODO: Add a full example from start to finish, like a tutorial on how to create a new endpoint.