docs(contributing): begin explaining contribution process

CONTRIBUTING.rst

+============================
+Contributing to Discuss Data
+============================
+
+As an open source project, Discuss Data welcomes contributions of many forms.
+
+Examples of contributions include:
+
+* Code patches
+* Documentation improvements
+* Bug reports and patch reviews

CONTRIBUTORS.txt

-Felix Herrmann, Stefan Hynek, Ubbo Veentjer
+Felix Herrmann
+Stefan Hynek
+Ubbo Veentjer

merge_production_dotenvs_in_dotenv.py

@@ -4,9 +4,7 @@ from typing import Sequence
 import pytest
 
 ROOT_DIR_PATH = os.path.dirname(os.path.realpath(__file__))
-PRODUCTION_DOTENVS_DIR_PATH = os.path.join(
-    ROOT_DIR_PATH, ".envs", ".production"
-)
+PRODUCTION_DOTENVS_DIR_PATH = os.path.join(ROOT_DIR_PATH, ".envs", ".production")
 PRODUCTION_DOTENV_FILE_PATHS = [
     os.path.join(PRODUCTION_DOTENVS_DIR_PATH, ".django"),
     os.path.join(PRODUCTION_DOTENVS_DIR_PATH, ".postgres"),