Make Compilers a subsection under Tools

Ref: #10

README.md

@@ -10,7 +10,7 @@ A list of actually decent, actually used AND appreciated in the industry C++ lib
 ## Tools
 * [`clang-format`](http://clang.llvm.org/docs/ClangFormat.html) - Highly integratable C/C++/Java/JavaScript/Objective-C/Protobuf code formatter from the Clang team.
 
-## Compilers
+### Compilers
 * [GNU GCC](https://gcc.gnu.org) - Part of the GNU Compiler Collection, and for many the reference in terms of C++ implementations.
 * [Clang](http://clang.llvm.org/) - A modern, modular C++ compiler, often the first to implement new C++ features. Bundled with [Xcode](https://developer.apple.com/xcode/) for Mac OS users.
 * [MinGW-w64](http://mingw-w64.org/doku.php) - A port of the GNU GCC compiler to Windows, offering almost everything the Linux version offers.