add beginnings of admin panel

README.md

@@ -24,6 +24,16 @@
 ## configuration
 
 transbeam is configured with the following environment variables:
+- `TRANSBEAM_ADMIN_PASSWORD_HASH`: Argon2 hash of a password for
+  accessing the admin interface. To generate:
+  ```bash
+  echo -n 'Password: '; head -1 | tr -d '\n' | argon2 $(openssl rand -base64 32) -id -t 2 -m 14 -p 1 -e
+  ```
+- `TRANSBEAM_COOKIE_SECRET`: Base64-encoded cryptographic random data
+  for encrypting private session cookies. To generate:
+  ```bash
+  openssl rand -base64 64 | tr -d '\n'
+  ```
 - `TRANSBEAM_STORAGE_DIR`: path where uploaded files should be stored
   (default: `./storage`)
 - `TRANSBEAM_STATIC_DIR`: path where the web app's static files live