Postclone script should replace "Your Plugin Name" reference in readme

[PeterStaev]

The first heading should be automatically replaced with the with the name of the plugin. Also the reference to <your-plugin-name> in the tns plugin add section should also be replaced with the actual plugin.

[romulowspp]

I created a PR and I hope I'm doing what was proposed! : D

[zbranzov]

@romulowspp Thanks for the PR and help provided to make NativesScript world better.