Add a Packit configuration for Fedora packaging (#1086)

* Add Packit configuration for Fedora packaging

 - all pull requests are build-tested in https://copr.fedorainfracloud.org
 - new releases will create pull requests in https://src.fedoraproject.org/rpms/httpie

Co-authored-by: Mickaël Schoentgen <contact@tiger-222.fr>

.gitignore

@@ -139,3 +139,8 @@ dmypy.json
 
 # Pyre type checker
 .pyre/
+
+# Packit
+/httpie.spec
+/httpie-*.rpm
+/httpie-*.tar.gz