Add link to GitHub and fix navigation order

docs/README.md

+---
+title: Theodolite
+nav_order: 1
+permalink: /
+---
+
 # Theodolite
 
 > A theodolite is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes.  -- <cite>[Wikipedia](https://en.wikipedia.org/wiki/Theodolite)</cite>

docs/_config.yml

 title: "Theodolite"
 remote_theme: pmarsceill/just-the-docs
 #color_scheme: "dark"
-#search_enabled: false
\ No newline at end of file
+aux_links:
+    "Theodolite on GitHub":
+      - "//github.com/cau-se/theodolite"
\ No newline at end of file