Improve some documentation (#78)

As reported in the Element Design room, there was a dead link in the README and the documentation about how to modify Compound was a bit lacking.

README.md

@@ -25,4 +25,4 @@ Tokens are exported to three platforms
 - [Development](./docs/development.md)
 - [Icons](./docs/icons.md)
 - [Release](./docs/release.md)
-- [Synchronise with Figma](./docs/sync-tokens.md)
+- [Synchronise with Figma](https://compound.element.io/?path=/docs/design-get-started--docs)

docs/development.md

@@ -1,9 +1,12 @@
 # 🤓 Development
 
 The tokens are defined under the `tokens/` folder and follow the [tokens.studio specification](https://docs.tokens.studio/tokens/json-schema).
-They are then transformed to the supported platforms using [Style Dictionary](https://amzn.github.io/style-dictionary/).
+Normally, our designers will update this folder by [syncing it with Figma](https://compound.element.io/?path=/docs/design-get-started--docs).
+But if you are maintaining a custom fork and wish to modify the tokens, you can also edit the JSON data in this folder directly.
 
-All consumable tokens are generated under `assets/`. Generate them by running
+The tokens are then transformed using [Style Dictionary](https://amzn.github.io/style-dictionary/) into formats which supported platforms can consume.
+These generated files live in the `assets/` folder, and the code that generates them can be found in `src/`.
+Generate them by running:
 
 ```
 yarn build