Missing step from Go documentation should be repeated here for clarity. The 'goexec' command will not work unless this step has been completed.

WebAssembly.md

@@ -95,12 +95,18 @@ $ goexec 'http.ListenAndServe(":8080", http.FileServer(http.Dir(".")))'
 
 Or use your own https://play.golang.org/p/pZ1f5pICVbV[basic HTTP server command].  
 
+Note: for the `goexec` command to work on Unix-like systems, you must [add the PATH environment variable](https://golang.org/doc/install#tarball) for Go to your shell's `profile`. Go's getting started guide explains this: 
+> Add /usr/local/go/bin to the PATH environment variable. You can do this by adding this line to your /etc/profile (for a system-wide installation) or $HOME/.profile:
+
+> `export PATH=$PATH:/usr/local/go/bin`
+
+> Note: changes made to a profile file may not apply until the next time you log into your computer
+
 Finally, navigate to http://localhost:8080/index.html, open the
 JavaScript debug console, and you should see the output. You can
 modify the program, rebuild `main.wasm`, and refresh to see new
 output.
 
-
 # Executing WebAssembly with Node.js
 
 It's possible to execute compiled WebAssembly modules using Node.js