docs: fix path to rspamd.log

[ap-wtioit]

Description

fix the remaining /var/log/supervisor/rspamd.log to also point the user to /var/log/mail/rspamd.log

Discovered this when i had to replace the log path in our local tests (using docker-mailserver with enabled rspamd to check if our mails conform to those non RFC rules). It seems this was missed in 894978d

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (README.md or the documentation under docs/)
• If necessary I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Info @wt-io-it

[github-actions]

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[georglauterbach]

Good catch! I should have greped for this in my PR.