Add Nushell completion script (#1571)

bin/generate-completions

@@ -4,5 +4,8 @@ set -euxo pipefail
 
 for script in completions/*; do
   shell=${script##*.}
+  if [ $shell == nu ]; then
+    continue
+  fi
   cargo run -- --completions $shell > $script
 done

completions/just.nu

@@ -0,0 +1,8 @@
+def "nu-complete just" [] {
+    (^just --dump --unstable --dump-format json | from json).recipes | transpose recipe data | flatten | where {|row| $row.private == false } | select recipe doc parameters | rename value description
+}
+
+# Just: A Command Runner
+export extern "just" [
+    ...recipe: string@"nu-complete just", # Recipe(s) to run, may be with argument(s)
+]