Update README to reflect that NotoColorEmoji is checked in.
Update README to reflect that NotoColorEmoji is checked in.

Formerly we included a statement that it had to be built first.

julroy67/noto-emoji,dougfelt/noto-emoji,julroy67/noto-emoji,googlei18n/noto-emoji,googlefonts/noto-emoji,googlei18n/noto-emoji,googlei18n/noto-emoji,dougfelt/noto-emoji,googlefonts/noto-emoji,dougfelt/noto-emoji,googlefonts/noto-emoji