Add security warning for cron token storage

docs/deployment.md

@@ -49,13 +49,43 @@ crontab -e
 0 0 * * * GH_TOKEN=ghp_your_token_here /home/youruser/.local/bin/ghrel check --since 1d >> /opt/nicible/ghrel.log 2>&1
 ```
 
+> [!WARNING]
+> **Never store your GitHub token as plaintext in crontab.** Crontab files may be readable by other users on the system. Use one of these alternatives instead:
+>
+> **Option 1: Environment file (recommended)**
+> Create a restricted environment file and source it from cron:
+> ```bash
+> echo 'GH_TOKEN=ghp_your_token_here' | sudo tee /etc/ghrel/token.env
+> sudo chmod 600 /etc/ghrel/token.env
+> ```
+> Then in crontab:
+> ```cron
+> 0 */6 * * * . /etc/ghrel/token.env && /home/youruser/.local/bin/ghrel check --since 6h >> /opt/nicible/ghrel.log 2>&1
+> ```
+>
+> **Option 2: Wrapper script**
+> Create a script with restricted permissions:
+> ```bash
+> cat > /opt/nicible/ghrel-check.sh << 'EOF'
+> #!/bin/bash
+> export GH_TOKEN="ghp_your_token_here"
+> exec /home/youruser/.local/bin/ghrel check --since 6h
+> EOF
+> chmod 700 /opt/nicible/ghrel-check.sh
+> ```
+> Then in crontab:
+> ```cron
+> 0 */6 * * * /opt/nicible/ghrel-check.sh >> /opt/nicible/ghrel.log 2>&1
+> ```
+>
+> **Option 3: Use systemd timer instead** (see below — preferred over cron)
+
 ### Notes
 
 - Always use the **full path** to `ghrel` — cron runs with a minimal `$PATH`
 - Use `2>&1` to capture both stdout and stderr in the log file
 - Ensure the log directory exists and is writable: `sudo mkdir -p /opt/nicible && sudo chown $USER /opt/nicible`
 - The `--since` flag should match or slightly exceed your cron interval to avoid missing entries
-- Consider storing `GH_TOKEN` in a separate file and sourcing it from cron to avoid plaintext exposure
 
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