gnu: parallel: Separate out the doc directory.

* gnu/packages/parallel.scm (parallel)[outputs]: Add doc.
[arguments]: Add configure-flags.

Change-Id: I3a3e57a60d4e2089be9a04505f1756ccbb2300ce

gnu/packages/parallel.scm

@@ -81,6 +81,7 @@
   (package
     (name "parallel")
     (version "20251122")
+    (outputs '("out" "doc"))
     (source
      (origin
       (method url-fetch)
@@ -101,7 +102,10 @@
                        "src/parallel_cheat_bw.pdf")))))
     (build-system gnu-build-system)
     (arguments
-     `(#:phases
+     `(#:configure-flags
+       (list (string-append "--docdir=" (assoc-ref %outputs "doc")
+                             "/share/doc/parallel"))
+       #:phases
        (modify-phases %standard-phases
          (add-after 'unpack 'patch-bin-sh
            (lambda _