Merge pull request finos#974 from kriswest/724-npm-proxy-config-instructions

docs: add note on npx proxy configuration

Author: JamieSlome

website/docs/usage.mdx

@@ -28,3 +28,9 @@ npx -- @finos/git-proxy
 ```bash
 npx -- @finos/git-proxy-cli
 ```
+
+If you use a proxy server to access `npm` then please note that you also need to configure your proxy for `npx` before running the above commands:
+
+```bash
+npx config set https-proxy <company-proxy-endpoint>
+```