Created Customize Filer Store (markdown)

Customize-Filer-Store.md

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+It is fairly easy if you need to store filer metadata with other data store.
+
+Let's use "yourstore" as the chosen name.
+
+Here are the steps:
+1. add a package under github.com/chrislusf/seaweedfs/weed/filer2/yourstore
+2. implement the filer2.FilerStore interface
+```
+package filer2
+
+import (
+	"errors"
+)
+
+type FilerStore interface {
+	GetName() string
+	// Initialize initializes the file store
+	Initialize(configuration Configuration) error
+	InsertEntry(*Entry) error
+	UpdateEntry(*Entry) (err error)
+	FindEntry(FullPath) (entry *Entry, err error)
+	DeleteEntry(FullPath) (err error)
+	ListDirectoryEntries(dirPath FullPath, startFileName string, includeStartFile bool, limit int) ([]*Entry, error)
+}
+
+```
+3. Remember to add yourstore to the list of supported stores
+```
+func init() {
+	filer2.Stores = append(filer2.Stores, &YourStore{})
+}
+```
+4. Load yourstore. Just import it in  github.com/chrislusf/seaweedfs/weed/server/filer_server.go
+```
+import (
+	"net/http"
+	"strconv"
+	"github.com/chrislusf/seaweedfs/weed/filer2"
+	_ "github.com/chrislusf/seaweedfs/weed/filer2/cassandra"
+	_ "github.com/chrislusf/seaweedfs/weed/filer2/leveldb"
+	_ "github.com/chrislusf/seaweedfs/weed/filer2/memdb"
+	_ "github.com/chrislusf/seaweedfs/weed/filer2/mysql"
+	_ "github.com/chrislusf/seaweedfs/weed/filer2/postgres"
+	_ "github.com/chrislusf/seaweedfs/weed/filer2/redis"
+	_ "github.com/chrislusf/seaweedfs/weed/filer2/yourstore"
+        // ^^ add here
+	"github.com/chrislusf/seaweedfs/weed/security"
+	"github.com/chrislusf/seaweedfs/weed/glog"
+)
+
+```