fix typo in docstring

Author: Jeff Whitaker

src/netCDF4/_netCDF4.pyx

@@ -1050,7 +1050,7 @@ are collective.  There are a couple of important limitations of parallel IO:
    to write to it.
  - You cannot use variable-length (VLEN) data types.
 
-***Import warning regarding threads:***  The underlying netcdf-c library is not thread-safe, so netcdf4-python cannot perform parallel
+***Important warning regarding threads:***  The underlying netcdf-c library is not thread-safe, so netcdf4-python cannot perform parallel
 IO in a multi-threaded environment.  Users should expect segfaults if a netcdf file is opened on multiple threads - care should
 be taken to restrict netcdf4-python usage to a single thread, even when using free-threaded python.