fix: Fix link to EW in README file (#3149)

Author: willdurand

README.md

@@ -16,7 +16,7 @@ cross-platform way. Initially, it will provide a streamlined experience for deve
 ## Documentation
 
 - [Getting started with web-ext][web-ext-user-docs]
-- [Command reference](https://extensionworkshop.com/documentation/develop/web-ext-command-reference)
+- [Command reference](https://extensionworkshop.com/documentation/develop/web-ext-command-reference/)
 
 Here are the commands you can run. Click on each one for detailed documentation or use `--help` on the command line, such as `web-ext build --help`.