docs: Add sunos to the reference table
I originally liked "solaris", but I've changed my mind. Both illumos
(the open-source fork of OpenSolaris) and Oracle's closed-source
Solaris are identified by the same token, and there are differences
between them; so using "sunos" as a sort "supertype" for both makes
sense to me.
@@ -96,6 +96,7 @@ These are provided by the `.system()` method call.
| linux | |
| netbsd | |
| windows | Any version of Windows |
+| sunos | illumos and Solaris |
Any string not listed above is not guaranteed to remain stable in
future releases.
