readme.md: prepare Markdown for GitHub and Doxygen rendering

readme.md

-# RapidJSON
+# RapidJSON {#mainpage}
 
 Copyright (c) 2011-2014 Milo Yip (miloyip@gmail.com)
 
@@ -37,7 +37,7 @@ Users can build and run the unit tests on their platform/compiler.
 
 ## Installation
 
-RapidJSON is a header-only C++ library. Just copy the `rapidjson/include/rapidjson` folder to system or project's include path.
+RapidJSON is a header-only C++ library. Just copy the `include/rapidjson` folder to system or project's include path.
 
 To build the tests and examples:
 
@@ -45,15 +45,21 @@ To build the tests and examples:
 2. Copy premake4 executable to RapidJSON/build (or system path)
 3. Run `rapidjson/build/premake.bat` on Windows, `RapidJSON/build/premake.sh` on Linux or other platforms
 4. On Windows, build the solution at `rapidjson/build/vs2008/` or `/vs2010/`
-5. On other platforms, run GNU make at `rapidjson/build/gmake/` (e.g., `make -f test.make config=release32`, `make -f example.make config=debug32`)
+5. On other platforms, run GNU make at `rapidjson/build/gmake/` (e.g., `make -f test.make config=release32`; `make -f example.make config=debug32`)
 6. On success, the executable are generated at `rapidjson/bin`
 
+To build the [Doxygen](http://doxygen.org) documentation:
+
+1. Obtain and install [Doxygen](http://doxygen.org/download.html).
+2. In the top-level directory, run `doxygen build/Doxyfile`.
+3. Browse the generated documentation in `doc/html`.
+
 ## Usage at a glance
 
 This simple example parses a JSON string into a document (DOM), make a simple modification of the DOM, and finally stringify the DOM to a JSON string.
 
 [simpledom.cpp](example/simpledom/simpledom.cpp)
-```cpp
+~~~~~~~~~~cpp
 #include "rapidjson/document.h"
 #include "rapidjson/writer.h"
 #include "rapidjson/stringbuffer.h"
@@ -80,12 +86,12 @@ int main() {
     std::cout << buffer.GetString() << std::endl;
     return 0;
 }
-```
+~~~~~~~~~~
 
 Note that this example did not handle potential errors.
 
 The following diagram shows the process.
 
-![simpledom](doc/diagram/simpledom.png?raw=true)
+![simpledom](doc/diagram/simpledom.png)
 
 More [examples](example/) are available.