Add yarn.lock, ignore node_modules

Fixes #14
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..3c3629e
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+node_modules
diff --git a/yarn.lock b/yarn.lock
new file mode 100644
index 0000000..fb57ccd
--- /dev/null
+++ b/yarn.lock
@@ -0,0 +1,4 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+
+