Add missing _sha3 module to Setup.dist (#2395)

diff --git a/Modules/Setup.dist b/Modules/Setup.dist
index 6b4c217..97c36db 100644
--- a/Modules/Setup.dist
+++ b/Modules/Setup.dist
@@ -253,6 +253,7 @@
 #_sha1 sha1module.c
 #_sha256 sha256module.c
 #_sha512 sha512module.c
+#_sha3 _sha3/sha3module.c
 
 # _blake module
 #_blake2 _blake2/blake2module.c _blake2/blake2b_impl.c _blake2/blake2s_impl.c