README: Add sol description

Author: matevz

README.md

@@ -5,12 +5,17 @@ site.
 
 ## `gh-pages` organization
 
-- `js`: holds JavaScript and TypeScript packages named after the package name
-  deployed at npmjs.org, but with stripped `@oasisprotocol/` prefix. For example
-  `@oasisprotocol/client` is hosted inside `js/client` path.
-- `rust`: holds Rust packages named after the import name of the package e.g.
-  `oasis_runtime_sdk`.
+- `js`: contains API reference for JavaScript and TypeScript packages named
+  after the package name deployed at npmjs.org, but with stripped
+  `@oasisprotocol/` prefix. For example `@oasisprotocol/client` is hosted
+  inside `js/client` folder.
+- `sol`: contains API reference for Solidity packages named after the package
+  name deployed at npmjs.org, but with stripped `@oasisprotocol/` prefix. For
+  example `@oasisprotocol/sapphire-contracts` is hosted inside
+  `sol/sapphire-contracts`.
+- `rust`: contains API reference for Rust packages named after the import name
+  of the package e.g. `oasis_runtime_sdk`.
 
-The branch is periodically updated by fetching the content of `api-reference`
-branch of the `oasis-sdk`, `sapphire-paratime` and other relevant Oasis
-repositories.
+`gh-pages` branch is periodically updated by fetching the content of
+`api-reference` branch of the `oasis-sdk`, `sapphire-paratime` and other Oasis
+repositories in the future.