Add docker local dev instructions (#1195)

.prettierignore

@@ -1,2 +1,4 @@
 *.md
-*.lock
+*.lock
+.cache/
+public/

README.md

@@ -29,6 +29,17 @@ Please feel free to suggest any changes. See our [contributing guide](https://gi
     
     *Note: You'll also see a second link: `http://localhost:8000/___graphql`. This is a tool you can use to experiment with querying your data. Learn more about using this tool in the [Gatsby tutorial](https://www.gatsbyjs.org/tutorial/part-five/#introducing-graphiql).*
 
+It is also possible to use docker:
+
+```bash
+docker run -it --rm \
+    -w /app -v "$PWD":/app \
+    -p 8000-8001:8000-8001 \
+    -e INTERNAL_STATUS_PORT=8001 \
+    node:14-slim \
+    sh -c 'yarn && yarn start'
+```    
+
 ## Questions?
 
 ### [Join our Slack community.](https://join.slack.com/t/posthogusers/shared_invite/enQtOTY0MzU5NjAwMDY3LTc2MWQ0OTZlNjhkODk3ZDI3NDVjMDE1YjgxY2I4ZjI4MzJhZmVmNjJkN2NmMGJmMzc2N2U3Yjc3ZjI5NGFlZDQ)

package.json

@@ -13,7 +13,7 @@
     ],
     "scripts": {
         "build": "cross-env GATSBY_EXPERIMENTAL_PAGE_BUILD_ON_DATA_CHANGES=true gatsby build --log-pages",
-        "start": "gatsby develop",
+        "start": "gatsby develop -H 0.0.0.0",
         "format": "prettier --write \"**/*.{html,js,ts,tsx,json,yml,css,scss}\"",
         "test": "echo \"Error: no test specified\" && exit 1",
         "typegen": "kea-typegen write ."