Add build/ and dist/ to .gitingore

These directories contain artifacts generated by setuptools.
diff --git a/.gitignore b/.gitignore
index 85b36c7..291b535 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,3 +5,5 @@
 *.egg-info
 devlib/bin/scripts/shutils
 doc/_build/
+build/
+dist/