CONTRIBUTING.md: drop outdated hint, add a panic policy

Author: oech3

CONTRIBUTING.md

@@ -123,7 +123,7 @@ submit a patch!
 ### Don't `panic!`
 
 The coreutils should be very reliable. This means that we should never `panic!`.
-Therefore, you should avoid using `.unwrap()` and `panic!`. Sometimes the use of
+Therefore, you should avoid using `println!`, `.unwrap()` and `panic!`. Sometimes the use of
 `unreachable!` can be justified with a comment explaining why that code is
 unreachable.
 
@@ -260,9 +260,6 @@ you contribute must at least compile without warnings for all platforms in the
 CI. However, you can use `#[cfg(...)]` attributes to create platform dependent
 features.
 
-**Tip:** For Windows, Microsoft provides some images (VMWare, Hyper-V,
-VirtualBox and Parallels) for development [on their official download page](https://developer.microsoft.com/windows/downloads/virtual-machines/).
-
 ## Improving the GNU compatibility
 
 Please make sure you have installed