readme update from Lucas Malor @ mobileread

see http://www.mobileread.com/forums/showpost.php?p=2488740&postcount=979
add back emulator screen setting hint
add nightlybuild script reference
Merge pull request #80 from houqp/readme-fix

readme update from Lucas Malor @ mobileread
Merge pull request #79 from houqp/houqp-master

enable scroll for readerrolling
update koreader-base: add top and bottom margin in reflowed page
Merge pull request #81 from chrox/kctx_fix

update koreader-base: add top and bottom margin in reflowed page
add cpath in reader.lua
add activity indicator when configuring in reflow mode
For now pillow activityIndicator is used to draw animated waiting icon
at the upper left corner of the screen. So pillow service should be
enabled to use this feature, but eventually we should implement an
activity indicator that is independent of native system.
Merge pull request #82 from chrox/activity_indicator

add activity indicator when configuring in reflow mode