Update the eldoc instructions

Author: bbatsov

doc/configuration/eldoc.md

@@ -1,15 +1,25 @@
 # ElDoc
 
-## Configuring eldoc
+Eldoc is a buffer-local minor mode that helps with looking up Lisp
+documentation. When it is enabled, the echo area displays some useful
+information whenever there is a Lisp function or variable at point;
+for a function, it shows the argument list, and for a variable it
+shows the first line of the variable's documentation string.
 
-* Enable `eldoc` in Clojure buffers:
-
-```el
-(add-hook 'cider-mode-hook #'eldoc-mode)
-```
+CIDER provides a Clojure backend for ElDoc that works out-of-the box, as
+long as `eldoc-mode` is enabled.
 
 ![Eldoc](../images/eldoc.png)
 
+## Enabling ElDoc
+
+`global-eldoc-mode` is enabled by default in Emacs 25.1, so you don't really have
+to do anything to enable it.
+
+It will in both source and REPL buffers.
+
+## Configuring ElDoc
+
 * CIDER also would show the eldoc for the symbol at point. So in `(map inc ...)`
 when the cursor is over `inc` its eldoc would be displayed. You can turn off this
 behaviour by:

doc/repl/configuration.md

@@ -27,15 +27,6 @@ REPL buffer in the current window:
 (setq cider-repl-display-in-current-window t)
 ```
 
-## Eldoc
-
-Eldoc displays function signatures in the minibuffer as you're typing.
-It's extremely useful! Enable `eldoc` in REPL buffers like this:
-
-```el
-(add-hook 'cider-repl-mode-hook #'eldoc-mode)
-```
-
 ## Customizing the REPL prompt
 
 You can customize the REPL buffer prompt by setting