Terminal logging is now coloured only on an interactive terminal

The terminal logger always coloured its text, so output piped or
redirected to a file, and the systemd journal, got escape codes. It
now colours only an interactive terminal.

The service's logs can therefore go to the journal: logging.file is
now optional for it, and the unit's comments and the README say so.

deploy/job-search.service

@@ -12,13 +12,13 @@
 #   sudo systemctl daemon-reload
 #   sudo systemctl enable --now job-search
 #
-# /etc/job-search/config.yaml should set at least:
+# /etc/job-search/config.yaml should set the database:
 #   database:
 #       file: /var/lib/job-search/jobsearch.db
+# Logs go to the journal (journalctl -u job-search), unless logging.file is
+# set to log to a file instead, rotated with job-search.logrotate:
 #   logging:
 #       file: /var/log/job-search/job-search.log
-# Without logging.file, logs go to the journal (as coloured text). Rotate the
-# log file with job-search.logrotate:
 #   sudo install -m 644 job-search.logrotate /etc/logrotate.d/job-search
 #
 # After each upgrade, migrate the database before restarting: