Android build instruction

1. build
1. m - build all modules from the top of the tree
2. mm - build all of the modules in current directory
3. mmm - build all of the modules in the supplied directory
2. make
1. make systemimage - system.img
2. make ramdisk - ramdisk.img
3. make userdataimage - userdata.img
4. make snod - build system.img quickly without checking the dependency
3. misc
1. croot - change directory to the top of the tree
2. cgrep - grep on all local c/c++ files
3. jgrep - grep on all local java files
4. resgrep - grep on all local res/*.xml files
5. godir - go to directory containing a file.
6. printconfig - print the current build configuraiton