Add basic build instructions to the README

README.md

@@ -11,13 +11,40 @@ Binaries for Linux, Mac, and Windows are available at
   [GitHub](https://github.com/ninja-build/ninja/releases).
 Run `./ninja -h` for Ninja help.
 
-To build your own binary, on many platforms it should be sufficient to
-just run `./configure.py --bootstrap`; for more details see
-[the wiki](https://github.com/ninja-build/ninja/wiki).
-
 Installation is not necessary because the only required file is the
 resulting ninja binary. However, to enable features like Bash
 completion and Emacs and Vim editing modes, some files in misc/ must be
 copied to appropriate locations.
 
 If you're interested in making changes to Ninja, read CONTRIBUTING.md first.
+
+## Building Ninja itself
+
+You can either build Ninja via the custom generator script written in Python or
+via CMake. For more details see
+[the wiki](https://github.com/ninja-build/ninja/wiki).
+
+### Python
+
+```
+./configure.py --bootstrap
+```
+
+This will generate the `ninja` binary and a `build.ninja` file you can now use
+to built Ninja with itself.
+
+### CMake
+
+```
+cmake -Bbuild-cmake -H.
+cmake --build build-cmake
+```
+
+The `ninja` binary will now be inside the `build-cmake` directory (you can
+choose any other name you like).
+
+To run the unit tests:
+
+```
+./build-cmake/ninja_test
+```