Minor style fixes

Author: josesimoes

README.md

@@ -244,6 +244,6 @@ The **nanoFramework** Class Libraries are licensed under the [MIT license](LICEN
 This project has adopted the code of conduct defined by the Contributor Covenant to clarify expected behaviour in our community.
 For more information see the [.NET Foundation Code of Conduct](https://dotnetfoundation.org/code-of-conduct).
 
-### .NET Foundation
+## .NET Foundation
 
 This project is supported by the [.NET Foundation](https://dotnetfoundation.org).

README.zh-cn.md

@@ -243,6 +243,6 @@ client.Connect(clientId);
 该项目采用了贡献者公约定义的行为准则，以阐明我们社区中的预期行为。
 有关详细信息，请参阅 [.NET Foundation 行为准则](https://dotnetfoundation.org/code-of-conduct)。
 
-### .NET Foundation
+## .NET Foundation
 
 该项目由 [.NET Foundation](https://dotnetfoundation.org) 支持.