Update environment variable in example

Editor assessment

Update environment variable in example is doubly unspecific: which environment variable, and which example, are both left to the diff. The docs type is right and the bodyless form is acceptable for a small documentation edit, but the subject had room to name the variable and the page. No footer is needed, and hygiene is otherwise clean — imperative, no trailing period. The message is not wrong, merely uninformative: a reader cannot decide from the header whether the change concerns their setup, which is the practical test this subject fails marginally. Acceptable.