build: Cache Binder Build Step (#188)

Utilize GitHub action to cache the Binder build step. Only enable this
step on master so that we'll only build upon merge to master.

Author: yangchoo

.github/workflows/binder-cache.yml

@@ -0,0 +1,16 @@
+name: Cache Binder
+
+on:
+  push:
+    branches:
+    - master
+
+jobs:
+  Create-MyBinderOrg-Cache:
+    runs-on: ubuntu-latest
+    steps:
+    - name: cache binder build on mybinder.org
+      uses: jupyterhub/repo2docker-action@master
+      with:
+        NO_PUSH: true
+        MYBINDERORG_TAG: ${{ github.event.ref }}

CHANGELOG.rst

@@ -9,6 +9,7 @@ Added
 ~~~~~
 
 - isort for automatic import sorting
+- Binder build cache step
 
 Updated
 ~~~~~~~