It's a lovely scene and it's a bit of a pity that it didn't make it into the published Silmarillion.
Here's a slightly longer quote:
His [Finwe's] coming was unheralded and unforeseen; and when Indis saw Finwe climbing the paths of the Mountain, and the light of Laurelin was behind him as a glory, without forethought she sang suddenly in great joy, and her voice went up as a song of the lirulin in the sky.

[Sorry, edited for typo]