guix: modify-input: Recommend prepend instead of append.

* doc/guix.texi (Defining Package Variants): Document the "prepend" clause of
modify-inputs first.
* guix/packages.scm (modify-inputs): use "prepend" in the docstring.

Signed-off-by: Christopher Baines <mail@cbaines.net>

doc/guix.texi

@@ -8080,20 +8080,20 @@ following forms:
 @item (delete @var{name}@dots{})
 Delete from the inputs packages with the given @var{name}s (strings).
 
-@item (append @var{package}@dots{})
-Add @var{package}s to the end of the input list.
-
 @item (prepend @var{package}@dots{})
 Add @var{package}s to the front of the input list.
+
+@item (append @var{package}@dots{})
+Add @var{package}s to the end of the input list.
 @end table
 
 The example below removes the GMP and ACL inputs of Coreutils and adds
-libcap to the back of the input list:
+libcap to the front of the input list:
 
 @lisp
 (modify-inputs (package-inputs coreutils)
   (delete "gmp" "acl")
-  (append libcap))
+  (prepend libcap))
 @end lisp
 
 The example below replaces the @code{guile} package from the inputs of
@@ -8104,7 +8104,7 @@ The example below replaces the @code{guile} package from the inputs of
   (replace "guile" guile-2.2))
 @end lisp
 
-The last type of clause is @code{prepend}, to add inputs to the front of
+The last type of clause is @code{append}, to add inputs at the back of
 the list.
 @end deffn
 

guix/packages.scm

@@ -1176,9 +1176,9 @@ inputs of Coreutils and adds libcap:
 
   (modify-inputs (package-inputs coreutils)
     (delete \"gmp\" \"acl\")
-    (append libcap))
+    (prepend libcap))
 
-Other types of clauses include 'prepend' and 'replace'.
+Other types of clauses include 'append' and 'replace'.
 
 The first argument must be a labeled input list; the result is also a labeled
 input list."