Update README.md - Githubissues

Add installation guide for documentation purposes.

Pull Request Description

Documented the very basic steps to install lj-inventory for those who need to read it.

Pull Request Checklist:

[x] Have you followed the guidelines in our contributing document and Code of Conduct?
[x] Have you checked to ensure there aren't other open for the same update/change?
[x] Have you built and tested the resource in-game after the relevant change?

loljoshie / lj-inventory