docs: Add external links workaround

This patch adds some external links to the docs navigation section.
Since mdbooks doesn't support this by default, this adds a JS file as
workaround, which avoids forking the theme or writing an extension for
mdbooks.

References:
https://github.com/rust-lang/mdBook/issues/1354

docs/book.toml

@@ -12,3 +12,4 @@ src = "src"
 git-repository-icon = "fa-gitlab"
 git-repository-url = "https://git.shivering-isles.com/shivering-isles/infrastructure-gitops/-/tree/main/docs"
 edit-url-template = "https://git.shivering-isles.com/-/ide/project/shivering-isles/infrastructure-gitops/edit/main/-/docs/{path}"
+additional-js = ["external-links.js"]

docs/external-links.js

+(function () {
+  function createExternalLink(name, link) {
+    const nav = document.getElementsByClassName("chapter")
+    let li = document.createElement("li")
+    let a = document.createElement("a")
+    a.href = link
+    a.append(name)
+    li.classList = "chapter-item expanded"
+    li.append(a)
+    nav[0].append(li)
+  }
+
+  createExternalLink("Blog", "https://shivering-isles.com")
+  createExternalLink("Repository", "https://git.shivering-isles.com/shivering-isles/infrastructure-gitops")
+})();

docs/src/SUMMARY.md

@@ -27,3 +27,7 @@
   - [Matrix]()
   - [Nextcloud]()
   - [Registry]()
+
+---
+
+# Links