Improve README

Add better examples, show contrast with git, and explain why they're
interesting.

Also remove the mention of the wiki from the footer. Most of the
interesting content has been migrated to the manual.

README.md

@@ -12,29 +12,43 @@ based on their syntax.
 
 See [the manual](http://difftastic.wilfred.me.uk/) to get started.
 
-## Screenshots
+## Demo: Wrapping Expressions
+
+Difftastic understands expression nesting. If you wrap an expression
+in an if statement, difftastic understand that the inner values are
+unchanged.
+
+![Elisp screenshot](img/elisp.png)
+
+Compare this with git's default diff. It is confused by indentation
+changes, and doesn't know which additional closing paren has been added.
+
+![Elisp comparison screenshot](img/elisp_comparison.png)
+
+## Demo: Reflowing Code
+
+Difftastic is robust to code formatting changes. If you change how
+many items appear on a single line, difftastic will only show you
+items which have changed.
 
 ![Rust screenshot](img/rust.png)
 
-![C screenshot](img/c.png)
+In git's default diff, it's harder to see that `iter` and the curly
+braces are unchanged. It's also harder to see the affected line numbers.
 
-![Haskell screenshot](img/haskell.png)
+![Rust comparison screenshot](img/rust_comparison.png)
 
 <!--
 To regenerate these screenshots:
 
+$ git clone git@github.com:magnars/dash.el.git
+$ cd dash.el
+$ GIT_EXTERNAL_DIFF=difft git show --ext-diff 72675567c68f002d828945badbb07fe963d24b5d
+
 $ git clone git@github.com:rust-itertools/itertools.git
 $ cd itertools
 $ GIT_EXTERNAL_DIFF=difft git show --ext-diff 38805c6a882a9f00615078250ccc8c070c3a214d
 
-$ git clone git@github.com:stedolan/jq.git
-$ cd jq
-$ GIT_EXTERNAL_DIFF=difft git show --ext-diff 6306ac89667cf35f47ddc40aa0630546c57e387f
-
-$ git clone git@github.com:xmonad/xmonad.git
-$ cd xmonad
-$ GIT_EXTERNAL_DIFF=difft git show --ext-diff 6d661203d39e44d1dc2aa3a930381e6711d26d56
-
 -->
 
 ## Languages
@@ -91,8 +105,3 @@ details.
 
 Files in `sample_files/` are also under the MIT license unless stated
 otherwise in their header.
-
-## Further Reading
-
-The [wiki](https://github.com/Wilfred/difftastic/wiki) includes
-additional notes on alternative diffing techniques and tools.