Mention differences in utilization of whitespace in East Asian languages (in Zero-width space sub-section)

Fixes: commonmark-spec#643

Author: haqer1

spec.txt

@@ -626,7 +626,8 @@ For most use-cases requiring escapes it's worth considering using backslash
 escapes, but zero-width space can be useful sometimes as well (to change the
 meaning of a neighboring character).
 
-Zero-width space can be used to ensure emphasis in East Asian text:
+Given differences in utilization of whitespace, zero-width space can be used to
+ensure emphasis, etc. in East Asian text:
 
 ```````````````````````````````` example
 棕色*狐狸。*​跳过