Add hint position test, README entry about ligatures

[purajit]

I had an issue with hint positions being incorrect, and noticed it only happened in certain places.

$ echo "a0240913-ligatures-test"
s0240913-ligatures-test
$ echo "-d0240913-ligatures-test"
-f0240913-ligatures-test
$ echo "↳20q0240913-ligatures-test
↳20w0240913-ligatures-test

It's all about ligatures!

Add a test since none of the existing tests check for hint positioning. Added a troubleshooting
entry in the README as well.

As for actually solving this issue, we would need something like #162