Improve Markdown syntax in README.md file
Improve Markdown syntax in README.md file

Fix some markdown issue following the markdownlint specification (https://github.com/markdownlint/markdownlint)

skywinder/ActionSheetPicker-3.0,ChronicStim/ActionSheetPicker,ChronicStim/ActionSheetPicker,skywinder/ActionSheetPicker-3.0