Fix/improve docs.

Author: felixfontein

plugins/modules/acme_certificate_order_create.py

@@ -273,6 +273,7 @@
     challenges:
       description:
         - Information for different challenge types supported for this identifier.
+        - Note that the keys are not valid Jinja2 identifiers.
       type: dict
       contains:
         http-01:

plugins/modules/acme_certificate_order_info.py

@@ -136,7 +136,7 @@
         - Encoded in the date format defined in L(RFC 3339, https://www.rfc-editor.org/rfc/rfc3339).
       type: str
       returned: depending on order
-    notAfter (optional, string):
+    notAfter:
       description:
         - The requested value of the C(notAfter) field in the certificate.
         - Encoded in the date format defined in L(RFC 3339, https://www.rfc-editor.org/rfc/rfc3339).