Fix blurb import in the runpy interface

When `blurb` was being restructured, the import paths moved to deeper levels of the project layout. It was updated in the console scripts so invoking just the `blurb` command worked but `python -m blurb` didn't. This resulted in breaking the MSI installer smoke testing workflow in CPython's CI [[1]].

Blurb's own CI never invokes said interface, so it had no chance of catching the regression.

This patch corrects the import but does not make an attempt to improve testing.

[1]: python/cpython#121879

Author: webknjaz

src/blurb/__main__.py

@@ -1,5 +1,5 @@
-"""Run blurb using `python3 blurb/`."""
-import blurb
+"""Run blurb using ``python3 -m blurb``."""
+from blurb import blurb
 
 
 if __name__ == '__main__':