feat: Add images/videos when making visual changes to code review gui…

…delines (#695)

We're adding a new guideline to the code review guidelines, which is to include
screenshots or screencasts when making visual changes.

Why this change is helpful?

When making visual changes, include screenshots or screencasts to show the effect of the changes.
This will help the reviewer understand the changes and the impact of the changes. It's also
a good way to document the changes, and it can be used as a reference in the future.

When working with a designer or even a product manager that does have
the development environment set up, it's a good way to communicate the changes and let
them know what to expect, and even reviewing/suggesting changes before the code is merged.

This is a good practice to have, and it's a good way to document the changes.

code-review/README.md

@@ -58,6 +58,9 @@ Watch a presentation that covers this material from [Derek Prior at RailsConf 20
   - "It's like that because of these reasons. Would it be more clear if I rename this class/file/method/variable?"
 
 - **Extract some changes and refactoring into future tickets/stories**
+- **When making visual changes, include screenshots or screencasts to show the effect of the changes**
+  - You may want to consider before/after screenshots or screencasts whenever applicable.
+
 - **Link to the code review from the ticket/story**
   - "Ready for review: https://github.com/organization/project/pull/1"