Avoid plain "using PrecompileTools" in example

[nhz2]

According to JuliaLang/julia#42080

Doing using Foo in packages or code that you want to keep working with
updated dependencies is not recommended. The reason for this is if another
dependency starts to export one of the same names as Foo the code will
error due to an ambiguity in which package the name should be taken from.
Instead, explicitly list what names you want to use from Foo, for example:
using Foo: Foo, parsefile, readfile to get access bring Foo and two
functions parsefile and readfile into scope.

[codecov]

Codecov Report

Merging #31 (3071fef) into main (325b469) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #31   +/-   ##
=======================================
  Coverage   92.22%   92.22%           
=======================================
  Files           3        3           
  Lines          90       90           
=======================================
  Hits           83       83           
  Misses          7        7           

[DilumAluthge]

Thanks!