docs: Replace binary which with node-which in README.md (#97)

Author: DevDengChao

README.md

@@ -31,12 +31,15 @@ await which('node', { path: someOtherPath, pathExt: somePathExt })
 
 ## CLI USAGE
 
-Same as the BSD `which(1)` binary.
+Just like the BSD `which(1)` binary but using `node-which`.
 
 ```
-usage: which [-as] program ...
+usage: node-which [-as] program ...
 ```
 
+You can learn more about why the binary is `node-which` and not `which` 
+[here](https://github.com/npm/node-which/pull/67)
+
 ## OPTIONS
 
 You may pass an options object as the second argument.