diff --git a/README.md b/README.md
index 7bdb218..1e21466 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,23 @@ Wrapper around [mozilla/sops](https://github.com/mozilla/sops).
 
 `pipx install git+https://github.com/dtomlinson91/csops`
 
+## Configuration
+
+Either use a `config.yml` or use environment variables.
+
+If using a `config.yml` create this file in either `~/.config/csops/` or a custom directory. If using a custom directory set the environment variable `CSOPS_CONFIG` equal to this directory.
+
+### GCP KMS Key
+
+If using a `config.yml` set the `gcp_mks_key` under the `csops` header:
+
+```yml
+csops:
+    gcp_kms_key: projects/plex-mozilla-sops/locations/global/keyRings/sops/cryptoKeys/sops-key
+```
+
+Or set the environment variable `CSOPS_GCP_KMS_KEY="projects/plex-mozilla-sops/locations/global/keyRings/sops/cryptoKeys/sops-keys"`
+
 ## Usage
 
 Encrypt: `csops e test.log`