Document the possibility for command line argument env assignments

Reviewed-by: Andy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4818)

CHANGES

diff --git a/CHANGES b/CHANGES
index cbae96d..691cbcd 100644
--- a/CHANGES
+++ b/CHANGES
@@ -9,6 +9,10 @@
 
  Changes between 1.1.0f and 1.1.1 [xx XXX xxxx]
 
+  *) Make it possible to have environment variable assignments as
+     arguments to config / Configure.
+     [Richard Levitte]
+
   *) Add multi-prime RSA (RFC 8017) support.
      [Paul Yang]