Clarify Ur documentation

[tomjaguarpaw]

Perhaps change

Its use is restricted while an argument in a non-linear function is unrestricted.

to

Its use is restricted. By contrast, an argument in a non-linear function is unrestricted.

The former is easy to misinterpret as "Its use is restricted during the time period that an argument in a non-linear function is unrestricted", which is meaningless nonsense.

linear-base/src/Data/Unrestricted/Linear.hs

Line 7 in 16795c7

-- be used in a linear way. Its use is __restricted__ while

[aspiwack]

Sounds good to me. I'm back from my holiday. I can do it soon. But you can also scoop me and make a PR 🙂 .