improve doc for outputs and hardware

Changed my mind about "installer" as a first-class concept, at least
in the current implementation. Not every documented output is an
installer

doc/parse-options-outputs.fnl

@@ -2,10 +2,18 @@
 
 ;; (local { : view } (require :fennel))
 
-(local outputs (collect [k v (ipairs arg)]
-                 (values v true)))
+(fn output? [option]
+  (match option.loc
+    ["system" "outputs" & _] true
+    _ false))
 
-(each [_ option (ipairs (yaml.load (io.read "*a")))]
-  (when (. outputs option.name)
+(fn sorted-options [options]
+  (table.sort
+   options
+   (fn [a b] (< a.name b.name)))
+  options)
+
+(each [_ option (ipairs (sorted-options (yaml.load (io.read "*a"))))]
+  (when (and (output? option) (not option.internal))
     (print (.. ".. _" (string.gsub option.name "%." "-") ":") "\n")
     (print option.description)))