add url to npm in gitignore

.gitignore

@@ -7,7 +7,7 @@ npm-debug.log
 .jshintrc
 .vs/
 
-# npm install --prefix test adds files in the test folder.
+# npm install --prefix test adds files in the test folder (https://docs.npmjs.com/configuring-npm/folders.html#executables).
 # There are 2 kindsof files, those without extension and those with cmd extension.
 # To ignore files without a extension, following precedure is nessecary:
 # - ignore all files in the test folder