Fix link

PR-URL: nodejs/node-addon-api#481
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: NickNaso <nicoladelgobbo@gmail.com>

doc/prebuild_tools.md

@@ -2,7 +2,7 @@
 
 The distribution of a native add-on is just as important as its implementation.
 In order to install a native add-on it's important to have all the necessary
-dependencies installed and well configured (see the [setup](doc/setum.md) section).
+dependencies installed and well configured (see the [setup](setup.md) section).
 The end-user will need to compile the add-on when they will do an `npm install`
 and in some cases this could create problems. To avoid the compilation process it's
 possible to ditribute the native add-on in pre-built form for different platform