Clarify CI script needing to quote colons

doc/ci/yaml/README.md

@@ -379,6 +379,8 @@ job:
     - bundle exec rspec
 ```
 
+Sometimes, `script` commands will need to be wrapped in single or double quotes. For example, commands that contain a colon (`:`) need to be wrapped in quotes so that the YAML parser knows to interpret the whole thing as a string rather than a "key: value" pair. Be careful when using special characters (`:`, `{`, `}`, `[`, `]`, `,`, `&`, `*`, `#`, `?`, `|`, `-`, `<`, `>`, `=`, `!`, `%`, `@`, `\``).
+
 ### stage
 
 `stage` allows to group build into different stages. Builds of the same `stage`