Update README.md SMTP features and TLS support details

Revised the documentation for greater clarity: swapped the listed items for explicit and implicit SSL/TLS support, and detailed the supported SMTP authentication mechanisms in an itemized format. This ensures users understand all available options and configurations more clearly.

README.md

@@ -39,10 +39,16 @@ Here are some highlights of go-mail's featureset:
 * [X] Very small dependency footprint (mainly Go Stdlib and Go extended packages)
 * [X] Modern, idiomatic Go
 * [X] Sane and secure defaults
-* [X] Explicit SSL/TLS support
-* [X] Implicit StartTLS support with different policies
+* [X] Implicit SSL/TLS support
+* [X] Explicit STARTTLS support with different policies
 * [X] Makes use of contexts for a better control flow and timeout/cancelation handling
-* [X] SMTP Auth support (LOGIN, PLAIN, CRAM-MD, XOAUTH2, SCRAM-SHA-1(-PLUS), SCRAM-SHA-256(-PLUS))
+* [X] SMTP Auth support
+  * [X] CRAM-MD5
+  * [X] LOGIN
+  * [X] PLAIN
+  * [X] SCRAM-SHA-1/SCRAM-SHA-1-PLUS
+  * [X] SCRAM-SHA-256/SCRAM-SHA-256-PLUS
+  * [X] XOAUTH2
 * [X] RFC5322 compliant mail address validation
 * [X] Support for common mail header field generation (Message-ID, Date, Bulk-Precedence, Priority, etc.)
 * [X] Concurrency-safe reusing the same SMTP connection to send multiple mails