add upgrade information

Author: mikaelcom

UPGRADE-2.0.md

@@ -0,0 +1,35 @@
+# UPGRADE FROM 1.0 to 2.0
+
+The main change is that the property `$soapclient` in the abstract class `AbstractSoapClientBase` is no more static.
+
+**Previously**:
+```php
+class MyService extends AbstractSoapClientBase
+{
+    try {
+        $this->setResult(self::getSoapClient()->CreateQueue($body));
+        return $this->getResult();
+    } catch (\SoapFault $soapFault) {
+        $this->saveLastError(__METHOD__, $soapFault);
+        return false;
+    }
+}
+```
+
+`self::getSoapClient()` was used to access the SoapClient instance.
+
+**Now**:
+```php
+class MyService extends AbstractSoapClientBase
+{
+    try {
+        $this->setResult($this->getSoapClient()->CreateQueue($body));
+        return $this->getResult();
+    } catch (\SoapFault $soapFault) {
+        $this->saveLastError(__METHOD__, $soapFault);
+        return false;
+    }
+}
+```
+
+`$this->getSoapClient()` is now used to access the SoapClient instance.