You just need some anti-aliasing!
You can enable this in “Edit > Project Settings > Quality” and enabling Anti-Aliasing from there.
There’s also a script in Unity’s Standard Assets to add Anti-Aliasing effects to a single camera at: “Assets/Standard Assets/Effects/ImageEffects/Scripts/Antialiasing.CS”
But the Quality Settings are probably the best way to go unless you’re working with multiple cameras that need show different effects.
I should mention that it also looks like there’s some Ambient Occlusion going on in your referance image. This too can be found in the “ImageEffects” folder as a script.
Hope this is what you’re after!