add package.json and change instructions to be more consistent with other modules

[sdetweil]

go to the module folder, type npm init
hit enter all the way thru

then do npm install async --save

this will add the asunc module to the package.json.

add the commit then package.json to your module and
then change the instructions

git clone
cd MMM-PrayerTime
npm install

npm will check if the module is installed and add it if not. the USER doesn't have to understand WHY, or 'if this doesn't work'
add the readme.md to the commit, commit
and then push to github... it will help others...

also, the scripted update process (see here https://github.com/sdetweil/MagicMirror_scripts) checks for modules with dependencies package.,json and does some extra work
please help