doc: Update pango_glyph_string_index_to_x

What the docs were saying is no longer strictly true,
now that we are using font metrics. Update them, and
add an illustration.

1 files changed, 0 insertions, 0 deletions

diff --git a/docs/glyphstring-positions-dark.png b/docs/glyphstring-positions-dark.png
new file mode 100644
index 00000000..88b926cd
--- /dev/null
+++ b/docs/glyphstring-positions-dark.png