Update README

README.md

@@ -130,6 +130,11 @@ Once succesfully completed, you can see the docker image in the `Registry`sectio
 
         * Persistent Volume Claim
 
+        As a Docker image is immutable, you may need to define some persistent storage. In the case of a PostgreSQL container we need to persist the data of the database.
+        
+        We do this using a `Persistent Volume Claim`.
+        > You can see that we define an `accessModes`to `ReadWriteOnce`, this mean that the Persistent Volume will only be accessed by one container.
+
         ```yaml
         apiVersion: v1
         kind: PersistentVolumeClaim
@@ -147,6 +152,12 @@ Once succesfully completed, you can see the docker image in the `Registry`sectio
 
         * PostgreSQL secret
 
+        We are here defining the PostgreSQL basic parameters : username, password and database. This `Secret` will be reused later in `Deployments`.
+
+        > Note: the data have to be base64 encoded. This can be done online or by command line on MacOS or Linux
+
+        ![alt text](img/base64.png)
+
         ```yaml
         apiVersion: v1
         kind: Secret
@@ -154,12 +165,13 @@ Once succesfully completed, you can see the docker image in the `Registry`sectio
         name: postgresql-credentials
         type: Opaque
         data:
-        username: YWRtaW4=
-        password: MWYyZDFlMmU2N2Rm
-        database: XXXXXXXXXXXXXXXX
+        username: cG9sbHNfdXNlcgo=
+        password: c2xsb3BfYzNiaQo=
+        database: cG9sbHMK
         ```
 
         * PostgreSQL Deployment
+
         ```yaml
         apiVersion: extensions/v1beta1
         kind: Deployment