Add node modules and new code for release (#57)

Co-authored-by: taakleton <taakleton@users.noreply.github.com>

node_modules/is-wsl/index.d.ts

@@ -0,0 +1,15 @@
+/**
+Check if the process is running inside [Windows Subsystem for Linux](https://msdn.microsoft.com/commandline/wsl/about) (Bash on Windows).
+
+@example
+```
+import isWsl = require('is-wsl');
+
+// When running inside Windows Subsystem for Linux
+console.log(isWsl);
+//=> true
+```
+*/
+declare const isWsl: boolean;
+
+export = isWsl;