Add cordova-plugin-file to README

[Rakonda]

No description provided.

[vitaliy-bobrov]

@Rakonda I didn't add this plugin to readme, because file transfer plugins already has it as dependency

[almothafar]

@vitaliy-bobrov so I don't need to add cordova-plugin-file ?

I used a blog post that where I knew about this awesome plugin saying I have to install cordova-plugin-file

[vitaliy-bobrov]

you'll see that after file transfer plugin installation the file plugin will be installed as well in the console output

[vitaliy-bobrov]

@almothafar, could you give the link to blog post?)