docs(auth): added JWT secret env var docs (#1090)

relate to #1062

docs/docs/configuration/authentifications/jwt.md

@@ -1,7 +1,14 @@
 # JWT
 
-AKHQ uses JWT tokens to perform authentication.
-Please generate a secret that is at least 256 bits and change the config like this:
+AKHQ uses signed JWT tokens to perform authentication.
+
+Please generate a secret that is at least 256 bits.
+
+You can use one of the following methods to provide the generated secret to AKHQ.
+
+## Configuration File
+
+Provide the generated secret via the AKHQ `application.yml` via the following directive:
 
 ```yaml
 micronaut:
@@ -12,6 +19,13 @@ micronaut:
         signatures:
           secret:
             generator:
-              secret: <Your secret here>
+              secret: <your secret here>
 ```
 
+## Environment Variable
+
+Provide the generated secret via [Micronaut Property Value Binding](https://docs.micronaut.io/latest/guide/index.html#_property_value_binding) using the following environment variable for the execution environment of AKHQ:
+
+```bash
+MICRONAUT_SECURITY_TOKEN_JWT_SIGNATURES_SECRET_GENERATOR_SECRET="<your secret here>"
+```