Move from GPL-3.0 to Apache License 2.0

Move from GPL-3.0 to Apache License 2.0, the preferred licence in the CNCF/Kubernetes community, as discussed in #37

Author: philippemerle

README.md

@@ -436,6 +436,6 @@ Following figure shows the software architecture of **KubeDiagrams**.
 
 ## License
 
-This project is licensed under the GPL-3.0 license - see the [LICENSE](https://github.com/philippemerle/KubeDiagrams/blob/main/LICENSE) file for details.
+This project is licensed under the Apache 2.0 License - see the [LICENSE](https://github.com/philippemerle/KubeDiagrams/blob/main/LICENSE) file for details.
 
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