GH-6 Added installation instructions on README.md

[keithmifsud]

No description provided.

[moufmouf]

Hey Keith,

Thanks for the PR!
Just to be clear, this package is frozen, as we are currently favoring the container-interop/service-provider approach (the ultimate goal is to be able to put things in a container in a cross-framework compatible way).

If you want more information on where we are and where we are heading, check out this blog article:
https://www.thecodingmachine.com/psr-11-an-overview-of-interoperable-php-modules/

[keithmifsud]

@moufmouf Thanks once again for the update. I will also look into this later on. Meanwhile I will close #6 and will create a new issue to update the Readme so that the community knows this is frozen. Please feel free to close the new issue if you don't find it necessary, otherwise I'll submit another PR for it later on.