Update subclades labels to specify "S"
I realized that we need to disambiguate between 20C/501T (the spike mutation) and 20C/501T (the nuc mutation) if we're going to have automated clade lookup. Thus, I think we need to specify "S" as in 20C/S.501T.
20A/N.194L nuc 26735 T
20A/N.194L nuc 28854 T
-20B/484K nuc 10667 G
-20B/484K nuc 11824 T
-20B/484K nuc 23012 A
-20B/484K nuc 28628 T
+20B/S.484K nuc 10667 G
+20B/S.484K nuc 11824 T
+20B/S.484K nuc 23012 A
+20B/S.484K nuc 28628 T
-20C/501T nuc 11417 T
-20C/501T nuc 12850 G
-20C/501T nuc 21364 T
-20C/501T nuc 23064 C
+20C/S.501T nuc 11417 T
+20C/S.501T nuc 12850 G
+20C/S.501T nuc 21364 T
+20C/S.501T nuc 23064 C
