add proxies instruction in README.md

README.md

@@ -45,6 +45,9 @@ If compared to saving websites with `wget -mpk`, this tool embeds all assets as
  - `-s`: Silent mode
  - `-u`: Specify custom User-Agent
 
+## HTTPS and HTTP proxies
+Please set `https_proxy`, `http_proxy` and `no_proxy` environment variables.
+
 ## Related projects
  - `Pagesaver`: https://github.com/distributed-mind/pagesaver
  - `SingleFile`: https://github.com/gildas-lormeau/SingleFile