doc/filters: drawtext: add example of printing texts on same baseline

Height of canvas produced by drawtext varies depending on symbols in
text, so add example for printing separate texts aligned horizontally.

Wording suggested by Lou Logan <lou@lrcd.com>
Signed-off-by: Andrey Utkin <andrey.utkin@pb.com>
Signed-off-by: Lou Logan <lou@lrcd.com>

doc/filters.texi

@@ -7135,6 +7135,14 @@ FOD=5 # fade out duration
 ffplay -f lavfi "color,drawtext=text=TEST:fontsize=50:fontfile=FreeSerif.ttf:fontcolor_expr=ff0000%@{eif\\\\: clip(255*(1*between(t\\, $DS + $FID\\, $DE - $FOD) + ((t - $DS)/$FID)*between(t\\, $DS\\, $DS + $FID) + (-(t - $DE)/$FOD)*between(t\\, $DE - $FOD\\, $DE) )\\, 0\\, 255) \\\\: x\\\\: 2 @}"
 @end example
 
+@item
+Horizontally align multiple separate texts. Note that @option{max_glyph_a}
+and the @option{fontsize} value are included in the @option{y} offset.
+@example
+drawtext=fontfile=FreeSans.ttf:text=DOG:fontsize=24:x=10:y=20+24-max_glyph_a,
+drawtext=fontfile=FreeSans.ttf:text=cow:fontsize=24:x=80:y=20+24-max_glyph_a
+@end example
+
 @end itemize
 
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