Update README.md

fix import error

Merge remote-tracking branch 'origin/master' into master

add comment

use RecyclerView item click

recyclerView item click

rename DiffCallback

update NetworkStateManager

update state-ViewModel and callback-ViewModel write

update state-ViewModel and Request write

update UnPeekLiveData and SharedViewModel write

remove import androidx.lifecycle.observe

bump Lifecycle version to 2.3.0-alpha07

bump Kotlin version to 1.4.0

update gradle dependency