improve the document

Author: zilongshanren

README.md

@@ -71,9 +71,11 @@ We have one build script for each platform, they are under `build/platform{ios/m
 All of them share the same usage:
 
 ```
-./build.sh --libs=param1 --arch=param2 --mode=param3 --list
+./build.sh -p=param0 --libs=param1 --arch=param2 --mode=param3 --list
 ```
 
+- param0: specify a platform, only (ios, mac, android, linux and tizen ) are valid values.
+
 - param1:
     - use `all` to build all the 3rd party libraries, it will take you a very long time.
     - use comma separated library names, for example, `png,lua,jpeg,webp`,  no space between the comma.
@@ -89,12 +91,12 @@ All of them share the same usage:
 - list:
     - Use these option to list all the supported libraries.
 
-### For iOS Platform
+### Build png on iOS platform
 For building libpng fat library with all arch x86_64, i386, armv7, arm64 on release mode:
 
 ```
 cd build/ios
-./build.sh --libs=png
+./build.sh -p=ios --libs=png
 ```
 
 After running this command, it will generate a folder named `png`:
@@ -113,23 +115,23 @@ For building libpng fat library with arch armv7 and arm64 on debug mode:
 
 ```
 cd build/ios
-./build.sh --libs=png --arch=armv7,arm64 --mode=debug
+./build.sh -p=ios --libs=png --arch=armv7,arm64 --mode=debug
 ```
 
-### For Android Platform
-xxx document will be update later.
+### Build for Android arm64
+
+1. Download Android NDK r10c and set the ANDROID_NDK to point to the Android ndk r10c path. Don't forget to `source ~/.bash_profile`.
+
+2. Modify the android.ini config file. Change `cfg_default_build_api=21` and `cfg_default_gcc_version=4.9`.
+
+3. Pass `--arch=64` to build the libraries with arm64 support.
 
-### For Mac
-xxx document will be update later.
 
-### For Tizen
-xxx document will be update later.
+For other platforms and other libraries, it is more or less the same way except for some minor changes in `--arch` parameter and `-p` parameter.
 
-### For Linux
-xxx After testing these scripts on Linux, document will be update.
 
 ## How to build a DEBUG and RELEASE version
-xxx we need to improve the script to add debug and release options.
+You can add flag "--mode=[debug | release]" for building DEBUG and RELEASE version.
 
 ## How to do build clean?
 If you use `./build.sh` to build static libraries, there is no need to do clean. After generating the static library, script will delete the intermediate files.

build/main.ini

@@ -18,7 +18,7 @@ zlib_archive_alias=z
 freetype2_archive_alias=freetype
 
 #clean up flag
-cfg_is_cleanup_after_build=no
+cfg_is_cleanup_after_build=yes
 
 ##valide options
 cfg_valid_build_mode=(release debug)