Add instructions for usage from a Fragment.
Add instructions for usage from a Fragment.

Fixes #8.

jonzl/sample-zxing,j-mateo/zxing-android-embedded,ALenfant/zxing-android-embedded,0359xiaodong/zxing-android-embedded,renekaigen/zxing-android-embedded,dhosford/zxing-android-embedded,cnevinc/zxing-android-embedded,jemsnaban/zxing-android-embedded,BBBInc/zxing-android-embedded,dimoge/zxing-android-embedded,jonzl/sample-zxing,BugMaker/zxing-android-embedded,journeyapps/zxing-android-embedded,Promptus/zxing-android-minimal,movedon2otherthings/zxing-android-embedded,WangXiaoxi/zxing-android-minimal,binson1989/zxing-android-embedded,BugMaker/zxing-android-embedded,Promptus/zxing-android-minimal,jeason789/test_embedded,BugMaker/zxing-android-embedded,WangXiaoxi/zxing-android-minimal,jonzl/sample-zxing,tsdl2013/zxing-android-embedded,wudayu/zxing-android-embedded,youyi1314/zxing-android-embedded,praveen062/zxing-android-embedded