update readme (#5)

README.md

@@ -6,8 +6,7 @@ Utilies for editing Nexus(or Nexus compatible) devices boot.img , then you don't
 ## Prerequisite
 #### Host OS requirement:
 
-The unpacking task only works on Linux, the packing task can work on Linux & OSX.
-So the recommended OS is Linux.
+The recommended OS is Linux.
 
 #### Target Android requirement:
 
@@ -15,12 +14,6 @@ So the recommended OS is Linux.
 
 (2) These utilities are known to work for Nexus (or Nexus compatible) boot.img for the following Android releases:
 
-Branch: master
-
- - Android AOSP master
-
-Branch: Marshmallow
-
  - Marshmallow (API Level 23)
  - Lollipop (API Level 21,22)
 
@@ -53,19 +46,5 @@ You get the repacked boot.img at $(CURDIR):
 
     boot.img.signed
 
-## Advanced usage for ROM developers
-If you have full Android source code, and have set up environment by envsetup/lunch, then the "pack" task will use $ANDROID\_PRODUCT\_OUT/root as rootfs.
-
-    . build/envsetup.sh
-    lunch xx-userdebug
-    cd <path_to_Nexus_boot_image_editor>
-    ./gradew pack
-
-If you have a rooted Android device connected via adb, you can also flash it with "flash" task:
-
-    ./gradew flash
-
-This will update the updated boot.img to /dev/block/by-name/boot.
-
 ## example & test
 An example boot.img has been placed at **src/test/resources/boot.img**, which is extracted from Nexus 5x(code: bullhead) factory images from [Google](https://dl.google.com/dl/android/aosp/bullhead-mda89e-factory-29247942.tgz), you can take it as a quick start.