updated docs, version is 2.2 and explain changes

lib/ansible/modules/extras/notification/sendgrid.py

@@ -39,12 +39,16 @@ requirements:
 options:
   username:
     description:
-      - username for logging into the SendGrid account
-    required: true
+      - username for logging into the SendGrid account.
+      - Since 2.2 it is only required if api_key is not supplied.
+    required: false
+    default: null
   password:
     description:
       - password that corresponds to the username
-    required: true
+      - Since 2.2 it is only required if api_key is not supplied.
+    required: false
+    default: null
   from_address:
     description:
       - the address in the "from" field for the email
@@ -60,34 +64,48 @@ options:
   api_key:
     description:
       - sendgrid API key to use instead of username/password
-    version_added: 2.1
+    version_added: 2.2
+    required: false
+    default: null
   cc:
     description:
       - a list of email addresses to cc
-    version_added: 2.1
+    version_added: 2.2
+    required: false
+    default: null
   bcc:
     description:
       - a list of email addresses to bcc
-    version_added: 2.1
+    version_added: 2.2
+    required: false
+    default: null
   attachments:
     description:
       - a list of relative or explicit paths of files you want to attach (7MB limit as per SendGrid docs)
-    version_added: 2.1
+    version_added: 2.2
+    required: false
+    default: null
   from_name:
     description:
       - the name you want to appear in the from field, i.e 'John Doe'
-    version_added: 2.1
+    version_added: 2.2
+    required: false
+    default: null
   html_body:
     description:
       - whether the body is html content that should be rendered
-    version_added: 2.1
-    choices: [True, False]
+    version_added: 2.2
+    required: false
+    default: false
   headers:
     description:
       - a dict to pass on as headers
-    version_added: 2.1
-
+    version_added: 2.2
+    required: false
+    default: null
 author: "Matt Makai (@makaimc)"
+notes:
+    - since 2.2 username and password are not required if you supply an api_key.
 '''
 
 EXAMPLES = '''