L2SS-2063: Add certificate documentation

README.md

-# Cryptocoryne
+# Stingray
 
-![Build status](git@git.astron.nl:lofar2.0/cryptocoryne/badges/main/pipeline.svg)
-![Test coverage](git@git.astron.nl:lofar2.0/cryptocoryne/badges/main/coverage.svg)
+![Build status](git.astron.nl/lofar2.0/cryptocoryne/badges/main/pipeline.svg)
+![Test coverage](git.astron.nl/lofar2.0/cryptocoryne/badges/main/coverage.svg)
 <!-- ![Latest release](https://git.astron.nl/templates/python-package/badges/main/release.svg) -->
 
-An example repository of an CI/CD pipeline for building, testing and publishing a python package.
+Cryptocoryne registeres and renews certificates for the lofar.net domain based on consul service registrations.
 
 ## Installation
+
 ```
 pip install .
 ```
 
 ## Usage
-```python
-from lofar-cryptocoryne import cool_module
 
-cool_module.greeter()   # prints "Hello World"
+Cryptocoryne runs periodically on the central nomad cluster.
+
+Every 5 minutes, cryptocoryne queries all services registered within consul that have the tag `cert`.
+Then the certificate `<service_name>.lofar.net` is registered or renewed (if needed) and stored in the LOFAR vault.
+
+Services then have the option to retrieve the certificates from the vault using nomads job templating:
+```hcl
+template {
+  data = <<EOH
+{{with secret "lets-encrypt/certificates/<service_name>.lofar.net" -}}
+{{.Data.data.cert }}
+{{.Data.data.chain -}}
+{{end}}
+EOH
+  destination = "${NOMAD_SECRETS_DIR}/fullchain.cer"
+}
+template {
+  data = <<EOH
+{{with secret "lets-encrypt/certificates/<service_name>.lofar.net" -}}
+{{.Data.data.key -}}
+{{end}}
+EOH
+  destination = "${NOMAD_SECRETS_DIR}/key.key"
+}
 ```
-
 ## Contributing
 
 To contribute, please create a feature branch and a "Draft" merge request.
@@ -29,7 +50,7 @@ changes is done through `tox`.
 
 ```pip install tox```
 
-With tox the same jobs as run on the CI/CD pipeline can be ran. These
+With tox the same jobs as run on the CI/CD pipeline can be run. These
 include unit tests and linting.
 
 ```tox```