Updates README

- Updates README to include information about adding sponsor logos to the website

Author: exoticDFT

README.md

@@ -64,3 +64,18 @@ docker run --rm -it -p 4000:4000 \
 Change a source file, such as `index.html` for example, and save the changes. You will see Jekyll automatically regenerate the site,
 after which you can reload the page in your browser to see the rendered changes.
 
+## Adding logos to the website
+
+There is an `_include` file, `add-sponsor-logo.html`, that can be used to add a
+sponsor's logo anywhere on the website.
+You can use the function by calling:
+`{% include add-sponsor-logo.html sponsor_url="some_url" logo_file="logo-filename.png" logo_alt="Some alt text for users" %}`
+See the include file for details on the variable names.
+The logo files need to be added to the `assets/img/sponsor-logos/` directory.
+
+### Logos on the main page
+
+To add the sponsor logos to the main page, follow the same directions as above,
+but make sure the include call is in the correct tier section for the sponsor.
+For example, UIUC is a platinum sponsor, so they are added to the
+`<div class="row sponsor-platinum ...>` block.