[patch] minor, documentation. Do explicitly state not supporting challenge for wildcard (DNS-01) in README.md

[ZjYwMj]

I hope this patch is very straight forward, and speaks for itself.

--- a/README.md      2022-04-12 13:20:51.745119156 +0000
+++ b/README.md      2022-04-12 13:41:32.814461464 +0000
@@ -206,6 +206,11 @@
 * Don't allow this script to be able to read your domain private key!
 * Don't allow this script to be run as root!
 
+## Limitations
+
+1. Wildcard certificate, such as for *.example.com, requires DNS-01 challenges. Which this script does not support. Renew of a recently obtained certificate for a domain with a DNS-01 challenge (the authz is still valid) will also fail in a similar manner. More details are at [List out of index error](https://github.com/diafygi/acme-tiny/issues/247#), which is a closed issue.
+
 ## Staging Environment
 
 Let's Encrypt recommends testing new configurations against their staging servers,