Create README.md

README.md

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+# mesoneer-tls-certificate-watchbot
+
+A poorman's TLS certificate monitoring system. It leverages GitHub Actions to run a workflow daily to probe the TLS certificate of the sites and notify if the expiration date is near.
+
+## How it works
+
+The gist of this is the GitHub Action Workflow `tls-certificate-check.yaml` in `.github/workflows`.
+
+It basically, for each defined site, probe its TLS certificate, then -- depends on the expiration date, send a Slack notification if needed.
+
+## Sites
+
+All monitored sites are defined in `sites.json`. The structure is deadly simple:
+
+```json
+{
+  "sites": [
+    { "domain": "example.org", "port" : 443 },
+    { "domain": "another.example.org", "port": 8443 }
+  ]
+}
+```
+
+## Monitoring Logs
+
+The workflow will add a Git commit every time it runs (to ensure that the repo is always active). The file `executions.jsonl` is also appended with a JSON line containing the result of the check.
+
+NOTE: JSONL - https://jsonlines.org/ - is used as it suits the purpose.