Add shorthand for installing scripts via bundle/add-bin.

Establishing a convention for scripts is beneficial for various tools.
However, we do not install scripts on anyones PATH - instead they go
to a self contained (dyn *syspath*) /bin folder which could be added to
path, or symlinks could be added.

src/boot/boot.janet

@@ -4337,6 +4337,15 @@
         absdest)
       :file (bundle/add-file manifest src dest chmod-mode)))
 
+  (defn bundle/add-bin
+    `Shorthand for adding scripts during an install. Scripts will be installed to
+    (string (dyn *syspath*) "/bin") by default and will be set to be executable.`
+    [manifest src &opt dest chmod-mode]
+    (default dest (string "bin" (sep) (->> src (string/split "/") last)))
+    (default chmod-mode 8r755)
+    (os/mkdir (string (dyn *syspath*) (sep) "bin"))
+    (bundle/add-file manifest src dest chmod-mode))
+
   (defn bundle/update-all
     "Reinstall all bundles"
     [&keys configs]