Clarify that DO_NOT_TRACK only disables telemetry for 1 or true

Author: kburym

content/github-cli/github-cli/github-cli-telemetry.md

@@ -105,7 +105,7 @@ You can opt out of the telemetry you see in the `log` mode described above using
 export GH_TELEMETRY=false
 ```
 
-Any falsy value works: `0`, `false`, `disabled`, or an empty string. You can also use the `DO_NOT_TRACK` convention:
+Any falsy value works: `0`, `false`, `disabled`, or an empty string. You can also use the `DO_NOT_TRACK` convention. Only the values `1` and `true` (case-insensitive) disable telemetry with `DO_NOT_TRACK`; other values are ignored:
 
 ```shell
 export DO_NOT_TRACK=true