Tell people that they are going to do a hard reset.

* magit.el (magit-reset-head): Reflect it in the prompt whether this
is going to be a hard reset or not.  Added optional argument instead
of using current-prefix-arg directly.
* magit.texi: Document it.

magit.el

@@ -1995,13 +1995,16 @@ in log buffer."
 
 ;;; Resetting
 
-(defun magit-reset-head (rev)
-  (interactive (list (magit-read-rev "Reset head to"
+(defun magit-reset-head (rev &optional hard)
+  (interactive (list (magit-read-rev (format "%s head to"
+					     (if current-prefix-arg
+						 "Hard reset"
+					       "Reset"))
 				     (or (magit-default-rev)
-					 "HEAD^"))))
+					 "HEAD^"))
+		     current-prefix-arg))
   (if rev
-      (magit-run-git "reset" (if current-prefix-arg
-				 "--hard" "--soft")
+      (magit-run-git "reset" (if hard "--hard" "--soft")
 		     (magit-rev-to-git rev))))
 
 (defun magit-reset-working-tree ()

magit.texi

@@ -388,6 +388,11 @@ Type @kbd{X} to reset your working tree and staging area to the most
 recently committed state.  This will discard your local modifications,
 so be careful.
 
+You can give a prefix to @kbd{x} if you want to reset both the current
+head and your working tree to a given commit.  This is the same as
+first using an unprefixed @kbd{x} to reset only the head, and then
+using @kbd{X}.
+
 @node Stashing
 @chapter Stashing