Add note about http01 and wildcard certificates

Fixes #757.

docs/reference/issuers.rst

@@ -34,8 +34,8 @@ An example of an Issuer type is ACME. A simple ACME issuer could be defined as:
 This is the simplest of ACME issuers - it specifies no DNS-01 challenge
 providers. HTTP-01 validation can be performed through using Ingress
 resources by enabling the HTTP-01 challenge mechanism (with the ``http01: {}``
-field). More information on configuring ACME Issuers can be in later sections
-of this document.
+field). More information on configuring ACME Issuers can be found :doc:`here <issuers/acme/index>`.
+
 
 ***********
 Namespacing

docs/reference/issuers/acme/http01.rst

@@ -25,5 +25,10 @@ using Ingress resources
          name: example-issuer-account-key
        http01: {}
 
+
+.. note::
+   Let's Encrypt does not support issuing wildcard certificates with HTTP-01 challenges.
+   To issue wildcard certificates, you must use the DNS-01 challenge.
+
 .. todo::
    Write a full description of how HTTP01 challenge validation works