Add gitpod.yml (dagster-io#7088)

Author: petehunt

.gitpod.yml

@@ -0,0 +1,17 @@
+tasks:
+- init: |
+    python3 -m venv /workspace/venv
+    source /workspace/venv/bin/activate
+    make dev_install
+    cd /workspace
+    zip -qr venv.zip venv
+    rm -fr venv
+- command: |
+    cd /workspace
+    unzip -q venv.zip
+    source /workspace/venv/bin/activate
+    cd /workspace/dagster
+
+ports:
+  - port: 3000
+    onOpen: open-browser