Pre commit instructions

.pre-commit-config.yaml

@@ -0,0 +1,8 @@
+- repo: local
+  hooks:
+      - id: black
+        name: black
+        entry: black
+        language: python
+        language_version: python3
+        types: [python]

README.md

@@ -48,6 +48,17 @@ cd prefect
 pytest
 ```
 
+### Black formatting
+
+Merging to master in Prefect requires your code to pass [black](https://github.com/ambv/black). This can be easy to forget when developing, and for that reason some developers may choose to install a pre-push hook for black, as follows:
+```
+pip install pre-commit # installs pre-commit package
+cd prefect/ # make sure you are in the root directory of the prefect repo
+pre-commit install --hook-type pre-push # creates necessary git hook files
+```
+There is already a pre-commit config file contained in the repo that creates the pre-push hook for black.  Now, you won't be allowed to `git push` without passing black.
+
+
 ### Build documentation
 
 To view documentation locally:

setup.py

@@ -6,7 +6,7 @@
 
 install_requires = [
     "click >= 6.7, < 7.0",
-    "cloudpickle >= 0.5.3, < 0.6.0",
+    "cloudpickle == 0.5.3",
     "croniter >= 0.3.23, < 0.4",
     "cryptography >= 2.2.2, < 3.0",
     "dask >= 0.18, < 0.19",