add documentation

README.md

@@ -1,2 +1,35 @@
 # gs-backup
-Google Cloud storage encrypted backup
+Encrypt a file and upload it to Google Cloud storage.
+
+## Required environment variables
+
+ * `BACKUP_FILE`: path to a file that should be uploaded.
+ * `BACKUP_BUCKET`: bucket url like gs://awesome-backups
+ * `BACKUP_PGP_KEY`: path to public key, defaults to /pubkey.asc
+
+## Volumes
+
+ * `/scratch`: temporary storage
+ * `/.config`: gcloud config
+
+## Usage
+
+Authenticate with service account (if the `/.config` volume is permanent this only needs to be done once):
+```
+docker run -i --rm \
+  -v /PATH/TO/gcloud-config/:/.config \
+  -v /PATH/TO/:/key.json \
+  gs-backup \
+  gcloud auth activate-service-account --key-file=/key.json
+```
+
+Run:
+```
+docker run -i --rm \
+  -v /PATH/TO/gcloud-config/:/.config \
+  -v /PATH/TO/paperhive-backups.pub.asc:/pubkey.asc \
+  -v /PATH/TO/data:/data \
+  -e BACKUP_FILE=/data/file \
+  -e BACKUP_BUCKET=gs://awesome-backups \
+  gs-backup
+```