Update README with usage guidance.

Closes #2

README.md

@@ -17,41 +17,23 @@ JavaScript are compiled and minified on GitHub Actions.
 
 ## Installation
 
-To install this package locally, you can use `install_github()` within `rterm`.
-
-```r
-# Remove existing varnish, if it has already been installed by The Carpentries sandpaper.
-remove.packages("varnish")
-# Install and import devtools, to make install_github() available
-install.packages("devtools")
-library("devtools")
-# Install this package from GitHub
-install_github("Robadob/carpentries-varnish")
-```
-
-There is no need to call this package directly, [{sandpaper}] will detect it and
-copy the styling and templates to your lesson website.
-
-If you wish to use this theme on GitHub pages, it is necessary to update a
-GitHub action provided in your Carpentries workbench repository.
+This fork of varnish should **not** be used in official carpentries repositories,
+it is intended for internally developed courses at the University of Sheffield.
 
-The below step should be added to `.github/workflows/sandpaper-main.yaml`
-directly before the final "Deploy Site" step.
+In order to use this fork of varnish you must update `config.yaml` to include the
+below lines (update `[user]` and `[repo]` as necessary, or replacing the line with
+a custom domain if required).
 
 ```yaml
-
-      - name: "Install Uni of Sheffield themed varnish"
-        run: |
-          remove.packages("varnish")
-          install.packages("devtools")
-          library("devtools")
-          install_github("Robadob/carpentries-varnish")
-        shell: Rscript {0}
+varnish: robadob/carpentries-varnish@main
+url: '[user].github.io/[repo]'
 ```
 
-*The Carpentries documentation does state that Varnish can be overridden,
-however the process for doing so is not documented. Hence, there may be a cleaner
-method discovered in future.*
+There is no need to call this package directly, once `config.yaml` has been updated
+[{sandpaper}] will detect it and copy the styling and templates to your lesson website.
+
+Once `config.yaml`, typical guides from The Carpentries can be followed to deploy
+locally or to GitHub pages.
 
 ## CSS and JavaScript