Update README with instruction

[hozza]

First of call, great plugin! 👍 🥇

While tinkering I noticed that the the README could do with an update in the New Highlights section as well as the installation instruction #34.

It currently reads as though all the params for adding a new comment type including color.name and color.foreground should be applied in the user settings. When it seems the color info is applied in the manual theme override section in theme_name.sublime-color-scheme as

{
  "name": "REVIEW COMMENTS",
  "scope": "comments.review",
  "foreground": "var(undefined_comment)",
  "background": "var(--background)",
},

And the new highlight settings are applied in the user settings for the plugin:

"REVIEW": {
  "scope": "comments.review",
  "identifier": "REVIEW",
  "ignorecase": true,
},