readme: better clarify steps for running the test

[Felanbird]

changed the wording a little bit and also moved the second sentence it's own number, both changes are for making sure you don't read past the full stop, and skip the running the test part of the step

also host the imgur link on github just because i'm already here

[runelite-github-app[bot]]

Includes non-plugin changes

[Felanbird]

this was more-or-less added in 207ee9c5b8518287ac1de967eb15cb2deb0e234a