[Bug]: Documentation error in CONTRIBUTING.md

### Duplicate ?

- [x] I have searched issues/discussions and did not find other issues/discussions reporting this bug.

### Product version

1.8.0

### Describe expected behavior

CONTRIBUTING.md claims that CoreWCF can be built using `dotnet build` from the `src` directory. This is untrue.

https://github.com/CoreWCF/CoreWCF/blob/main/CONTRIBUTING.md#building

### Describe actual behavior

I would expect the documentation to provide how-to build info that works.

### Which binding

NetTcp

### security

None

### Which .NET version

.NET 8

### Which os platform

Windows

### Code snippet used to reproduce the issue

```c#

```

### Stacktrace if any

```shell

```