Added a .dockerignore

Figured this would be useful while testing out 03572ae355

.dockerignore

@@ -0,0 +1,13 @@
+.DS_Store
+.cache
+.eggs
+.git
+.gitignore
+.ipynb_checkpoints
+.travis.yml
+build
+*.spec
+*.egg-info
+dist
+scratchpad
+venv

.gitignore

@@ -1,6 +1,8 @@
 build-metadata.json
 datasets.json
 
+scratchpad
+
 # SQLite databases
 *.db
 *.sqlite