Clarify sharing setup instructions in README (#595)

Author: Supakornn

README.md

@@ -61,4 +61,4 @@ docker build -t drawdb .
 docker run -p 3000:80 drawdb
 ```
 
-If you wish to work with sharing, set up [server](https://github.com/drawdb-io/drawdb-server) and environment variables according to `.env.sample`. This is not required unless you want to share files.
+If you want to enable sharing, set up the [server](https://github.com/drawdb-io/drawdb-server) and environment variables according to `.env.sample`. This is optional unless you need to share files..