test: Explain why test logging should be used

test/README.md

@@ -145,7 +145,7 @@ levels using the logger included in the test_framework, e.g.
   `test_framework.log` and no logs are output to the console.
 - when run directly, *all* logs are written to `test_framework.log` and INFO
   level and above are output to the console.
-- when run on Travis, no logs are output to the console. However, if a test
+- when run by [our CI (Continuous Integration)](/ci/README.md), no logs are output to the console. However, if a test
   fails, the `test_framework.log` and bitcoind `debug.log`s will all be dumped
   to the console to help troubleshooting.