Add see also for tutorial

Author: basnijholt

docs/source/index.md

@@ -5,6 +5,10 @@ end-before: summary-end
 ---
 ```
 
+```{seealso}
+[Click here](https://adaptive.readthedocs.io/en/latest/tutorial/tutorial.Learner1D.html) to start with the 1D function learning tutorial, the `adaptive.Learner1D`.
+```
+
 ```{include} ../../README.md
 ---
 start-after: references-start