Clarify "End Users" in the README

[costdev]

We were recently asked if end users had to install Git Updater in order to install a plugin, with this cited as confusing:

From the README:

Installation for End Users
Mini FAIR currently supports integration with Git Updater, with planned support for other tools such as EDD coming soon. To use Mini FAIR, install the latest version of plugin as well as a supported tool - that is, Git Updater.

In the context of a WordPress plugin, "End Users" would usually mean users of the plugin, as it does here. However, given the context of this plugin as being related to distributing plugins and themes, this section could do with some clarification.

[afragen]

To use the mini-fair plugin, yes Git Updater is required. Perhaps we should add a Required Plugins header. And then yes, just one more thing to fix depending on what we do with slugs.

[costdev]

To use the mini-fair plugin, yes Git Updater is required.

Yep, though the confusion was that a plugin author, in the context of WordPress, thought "end user" may refer to WordPress users rather than users of the mini-fair plugin.

I think it may be beneficial to clarify by replacing "end users" with "plugin/theme authors", or "package owners", for example.