Added dependencies. Updated readme.

.gitignore

@@ -1,8 +1,13 @@
+# See https://help.github.com/articles/ignoring-files/ for more about ignoring files.
+
 # dependencies
 /node_modules
 /.pnp
 .pnp.js
 
+# testing
+/coverage
+
 # next.js
 /.next/
 /out/
@@ -20,4 +25,10 @@ yarn-debug.log*
 yarn-error.log*
 
 # local env files
-.env*
+.env*
+
+# yarn
+.yarn/*
+!.yarn/releases
+!.yarn/plugins
+.pnp.*