add context to examples (#7)

Author: smaeda-ks

README.md

@@ -46,7 +46,9 @@ usage:
   workflows:
     use-my-orb:
       jobs:
-        - my-job
+        - my-job:
+            # You must use context for jobs require OIDC
+            context: my-context
 ```
 
 ## Example Vault configuration

src/examples/auth-oidc.yml

@@ -28,4 +28,5 @@ usage:
   workflows:
     use-my-orb:
       jobs:
-        - my-job
+        - my-job:
+            context: my-context