Added contribute section and gitpod config

.gitpod.yml

@@ -0,0 +1,7 @@
+tasks:
+    - before: nvm install 10 && nvm use 10
+      init: npm install
+      command: npm run start
+ports:
+    - port: 8080
+      onOpen: open-preview

README.md

@@ -35,3 +35,15 @@ Trilium is provided as either desktop application (Linux, Windows, Mac) or web a
 [See wiki for complete list of documentation pages.](https://github.com/zadam/trilium/wiki/)
 
 You can also read [Patterns of personal knowledge base](https://github.com/zadam/trilium/wiki/Patterns-of-personal-knowledge-base) to get some inspiration on how you might use Trilium.
+
+## Contribute
+
+Use a browser based dev environment
+
+[![Open in Gitpod](https://gitpod.io/button/open-in-gitpod.svg)](https://gitpod.io/#https://github.com/zadam/trilium)
+
+Or clone locally and run
+```
+npm install
+npm run start
+```