Requirements: add dev requirements and django-stubs.

requirements-dev.txt

@@ -0,0 +1,28 @@
+#
+# This file is autogenerated by pip-compile
+# To update, run:
+#
+#    pip-compile --output-file=requirements-dev.txt requirements.in/development.txt
+#
+appdirs==1.4.4            # via black
+asgiref==3.3.1            # via django
+black==20.8b1             # via -r requirements.in/development.txt
+click==7.1.2              # via black, pip-tools
+coverage==5.3.1           # via -r requirements.in/development.txt
+django-stubs==1.7.0       # via -r requirements.in/development.txt
+django==3.1.4             # via django-stubs
+mypy-extensions==0.4.3    # via black, mypy
+mypy==0.790               # via django-stubs
+pathspec==0.8.1           # via black
+pip-tools==5.4.0          # via -r requirements.in/development.txt
+pytz==2020.5              # via django
+pywatchman==1.4.1         # via -r requirements.in/development.txt
+regex==2020.11.13         # via black
+six==1.15.0               # via pip-tools
+sqlparse==0.4.1           # via django
+toml==0.10.2              # via black
+typed-ast==1.4.1          # via black, mypy
+typing-extensions==3.7.4.3  # via black, django-stubs, mypy
+
+# The following packages are considered to be unsafe in a requirements file:
+# pip

requirements.in/development.txt

@@ -1,4 +1,5 @@
 coverage
 pip-tools
 pywatchman
-black
+black
+django-stubs