Add example documentation

Fixes #13.

example/README.md

@@ -0,0 +1,36 @@
+# cppast - examples
+
+This directory contains example tools written using cppast.
+
+***Note:** These are not meant to be production ready tools, just a proof of concept!*
+
+All example executables get a single parameter,
+which is the directory where a `compile_commands.json` file is located.
+This file is a compilation database, you can read more about it [here](https://clang.llvm.org/docs/JSONCompilationDatabase.html).
+CMake, for example, can generate on when the option `CMAKE_EXPORT_COMPILE_COMMANDS` is `ON`.
+
+The tools will parse each file in the database and process it.
+Output will be written to `stdout`.
+
+## List of examples:
+
+### `ast_printer.cpp`
+
+It is a very simplified implementation of the cppast tool, it will print an AST.
+This is the starting example, it showcases entity visitation.
+
+### `documentation_generator.cpp`
+
+It is a very simplified documentation generator.
+This showcases usage of the `cppast::code_generator`.
+
+### Attributes example
+
+* `comparison.cpp`
+* `documentation_generator.cpp`
+* `enum_category.cpp`
+* `enum_to_string.cpp`
+* `serialization.cpp`
+
+Those examples were created as a part of my talk [Fun With (User-Defined) Attributes](http://foonathan.net/meetingcpp2017.html).
+Check the talk video to learn more about them.