Adding some clarification on how the -c flag can be used (#79)

* Explain how the -c flag works in tandem with the -e flag

Explain that the cascade flag can be used together with the -e flag to parse env files from another folder.

* Fixed typo

Author: gunhaxxor

README.md

@@ -40,6 +40,10 @@ $ dotenv -e .env3 -e .env4 <command with arguments>
 Some applications load from `.env`, `.env.development`, `.env.local`, and `.env.development.local`
 (see [#37](https://github.com/entropitor/dotenv-cli/issues/37) for more information).
 `dotenv-cli` supports this using the `-c` flag for just `.env` and `.env.local` and `-c development` for the ones above.
+The `-c` flag can be used together with the `-e` flag. The following example will cascade env files located one folder up in the directory tree (`../.env` followed by `../.env.local`):
+```bash
+dotenv -e ../.env -c 
+```
 
 ### Setting variable from command line
 It is possible to set variable directly from command line using the -v flag: