Add a little into to readme

README.md

@@ -6,8 +6,72 @@ manipulation.
 
 Documentation can be found in the [`doc/`][1] directory.
 
-***Note: This project is experimental. There are no known bugs in the parser itself, but the API is
-subject to change.***
+***Note: This project is experimental, so the API is subject to change.***
 
+In a Nutshell
+-------------
+
+Basically, the parser does nothing more than turn some PHP code into an abstract syntax tree. ("nothing
+more" is kind of sarcastic here as PHP has a ... uhm, let's just say "not nice" ... grammar, which makes
+parsing PHP very hard.)
+
+For example, if you stick this code in the parser:
+
+```php
+<?php
+echo 'Hi', 'World';
+hello\world('foo', 'bar' . 'baz');
+```
+
+You'll get a syntax tree looking roughly like this:
+
+```
+array(
+    0: Stmt_Echo(
+        exprs: array(
+            0: Scalar_String(
+                value: Hi
+            )
+            1: Scalar_String(
+                value: World
+            )
+        )
+    )
+    1: Expr_FuncCall(
+        name: Name(
+            parts: array(
+                0: hello
+                1: world
+            )
+        )
+        args: array(
+            0: Arg(
+                value: Scalar_String(
+                    value: foo
+                )
+                byRef: false
+            )
+            1: Arg(
+                value: Expr_Concat(
+                    left: Scalar_String(
+                        value: bar
+                    )
+                    right: Scalar_String(
+                        value: baz
+                    )
+                )
+                byRef: false
+            )
+        )
+    )
+)
+```
+
+If you then stick that result into the pretty printer you'll get back PHP code again :)
+
+This is useful for a variety of situations where you want to deal with code programmatically, like static
+analysis, code preprocessing and code generation.
+
+So, that's it, in a nutshell. You can find everything else in the [docs][1].
 
  [1]: https://github.com/nikic/PHP-Parser/tree/master/doc