Add back-to-the-top link to readme (#2707)

Author: bravesasha

README.md

@@ -4582,3 +4582,5 @@ I hope you enjoy using `just` and find great success and satisfaction in all
 your computational endeavors!
 
 😸
+
+[🔼 Back to the top!](#just)

crates/generate-book/src/main.rs

@@ -161,7 +161,9 @@ fn main() -> Result {
       for event in &mut chapter.events {
         if let Event::Start(Tag::Link(_, dest, _)) | Event::End(Tag::Link(_, dest, _)) = event {
           if let Some(anchor) = dest.clone().strip_prefix('#') {
-            *dest = CowStr::Borrowed(&links[anchor]);
+            if anchor != "just" {
+              *dest = CowStr::Borrowed(&links[anchor]);
+            }
           }
         }
       }