Update README.md (#117)

* Update README.md

Show more clearly that the upgrade guide includes v2 to v3 changes

* Update README.md

Co-authored-by: Freek Van der Herten <[email protected]>

Author: flatcapco

README.md

@@ -22,7 +22,7 @@ We invest a lot of resources into creating [best in class open source packages](
 
 We highly appreciate you sending us a postcard from your hometown, mentioning which of our package(s) you are using. You'll find our address on [our contact page](https://spatie.be/about-us). We publish all received postcards on [our virtual postcard wall](https://spatie.be/open-source/postcards).
 
-### Upgrading to 2.0
+### Upgrading
 
 Please see [UPGRADING](UPGRADING.md) for details.