Move readme parts to their corresponding packages

filecache/README.md

@@ -0,0 +1,20 @@
+## File cache
+
+Package `file_cache` implements a helper function that would cache results of
+an expensive operation to a file. It would use file contents when the file exist
+and won't call the function again unless the file is deleted.
+
+```go
+import "github.com/localhots/gobelt/filecache"
+```
+
+```go
+ctx := context.Background()
+var items []Item
+filecache.Load(&items, "tmp/cache/items.json", func() {  
+    err := conn.Query(ctx, "SELECT * FROM items").Load(&items).Error()
+    if err != nil {
+        log.Fatalf("Failed to load items: %v", err)
+    }
+})
+```