docs: add instructions for npm release (#39)

superset-frontend/temporary_superset_ui/superset-ui-plugins-deckgl/README.md

@@ -24,6 +24,18 @@ Please read the
 which include development environment setup and other things you should know about coding in this
 repo.
 
+### Releasing
+
+Make sure you have commit rights to the main `superset-ui-plugins-deckgl` repo, have checked it out (NOT a fork!) and
+belong to the `superset-ui` org on npm (=can publish new versions).
+
+1. `yarn install`
+2. `yarn build`
+3. `yarn release-patch-version`. This will raise an error, but you should see a new commit and tag, e.g. `v0.4.8`
+4. go to the DeckGL directory: `cd packages/superset-ui-legacy-preset-chart-deckgl`
+5. make sure you're logged into npm: `npm whoami` should display your npm username.
+6. `npm publish`
+
 ### License
 
 Apache-2.0