Add UPGRADE.md

Author: Mikael Peigney

UPGRADE.md

@@ -0,0 +1,40 @@
+# UPGRADE FROM 1.x TO 2.0
+
+## PHP Version
+
+Version 2.0 now requires a supported PHP version, that is PHP 7.4 and >= 8.0
+
+## Public methods of `SPFCheck`
+
+The available methods of `SPFCheck` has changed.
+
+```php
+# removed
+public function isIPAllowed($ipAddress, $domain);
+# replaced by
+public function getIPStringResult(string $ipAddress, string $domain): string;
+
+# added
+public function getDomainSPFRecords(string $domainName): array;
+public function getResult(Query $query): Result;
+```
+
+## `DNSRecordGetter` moved to the `Mika56\SPFCheck\DNS` namespace
+
+```php
+# before
+use Mika56\SPFCheck\DNSRecordGetter;
+use Mika56\SPFCheck\SPFCheck;
+
+$checker = new SPFCheck(new DNSRecordGetter());
+
+# after
+use Mika56\SPFCheck\DNS\DNSRecordGetter;
+use Mika56\SPFCheck\SPFCheck;
+
+$checker = new SPFCheck(new DNSRecordGetter());
+```
+
+## `DNSRecordGetterDirect` moved to its own repository
+
+The class has been moved to [mika56/spfcheck-dns-direct](https://github.com/Mika56/PHP-SPF-Check-DNS-Direct). This removed the dependency on `purplepixie/phpdns`.