Remove warning about using unxip in your program

This is obviously at odds to vending libunxip. More specifically,
though, while unxip schedules all over the cooperative thread pool, most
clients seem to not really expect to use it heavily anyways (since they
are small wrappers around the API, perhaps with some UI). For those that
actually do plan to do work there, Swift Concurrency does an OK job of
having the work share available resources. I don't expect this to be a
major problem and those that it is one for can probably figure out how
to work around it themselves, or reach out and ask in the worst case.

README.md

@@ -33,8 +33,6 @@ $ make install
 
 The installation prefix is configurable via the `PREFIX` variable.
 
-unxip is not currently designed to be embedded directly into the address space of another application. While it would "work" (with minor modifications to allow linking) its implementation expects to be the only user of the cooperative thread pool and effectively takes it over, which may adversely affect other code that wishes to run on it. The recommended way to use unxip is spawning it as a subtask.
-
 ## Usage
 
 The intended usage of unxip is with a single command line parameter that represents the path to an XIP from Apple that contains Xcode. For example: