Remove most of build/, move generation to build/gen.py

Build now with `./build/gen.py && ninja -C out`. README.md updated.

Change-Id: I00be44215e4a0e203a2e1ff38867e17535701cad
Reviewed-on: https://gn-review.googlesource.com/1240
Reviewed-by: Brett Wilson <[email protected]>
diff --git a/README.md b/README.md
index 331f0d3..c7e1ad3 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,11 @@
 # GN
 
-GN is a meta-build system that generates [Ninja](https://ninja-build.org).
+GN is a meta-build system that generates build files for
+[Ninja](https://ninja-build.org).
+
+Get started with:
+
+  git clone https://gn.googlesource.com/gn
+  cd gn
+  build/gen.py
+  ninja -C out