Update the extension's readme.md & composer pkgs

[Niloys7]

Hello,
Thanks for creating such a beautiful framework. I would like to use it for my upcoming WordPress projects but I found some issues where I was stuck.
Example: I tried to install the "Underpin Custom Post Type Loader" ext for my plugin but it's give me a fatal error when I tried to the readme.MD introductions. when I check the core "Underpin" plugin I found that the latest version is not supported the "underpin()" function. but the ext's readme.md files are not updated or do not have details for how it's working with the latest version.

I found some issues too when I tried to load packages via composer.
Example: Unerpin doesn't have a version declared on composer but "Underpin Custom Post Type Loader" ext have set version 2.0 for Underpin https://i.imgur.com/FtlpsTw.png :(

• Niloy