update readme

README.md

@@ -1,2 +1,11 @@
-# omega-kernel
-EZ-FLASH OMEGA Kernel
+#EZ-FLASH OMEGA Kernel
+
+### How to build 
+
+    1.We use devkitARM_r47, you can use the current version or newer.
+    2.Set the following environment variables in system, or modify the value in build.bat, based on your installation path
+
+        PATH,DEVKITARM,DEVKITPRO,LIBGBA
+
+    3.Double click on build.bat under winodws. If it goes well, you will get ezkernel.gba
+    4.Rename the ezkernel.gba to ezkernel.bin, that is the omega kernel upgrade file