feat: add assets cache & fix manifest content type (#54)

* feat: add assets cache & fix manifest content type

* fix: manifest content-type

netlify.toml

@@ -10,3 +10,8 @@
   from = "/*"
   to = "/index.html"
   status = 200
+
+[[headers]]
+  for = "/manifest.webmanifest"
+  [headers.values]
+    Content-Type = "application/manifest+json"

public/_headers

@@ -0,0 +1,3 @@
+/assets/*
+  cache-control: max-age=31536000
+  cache-control: immutable