Add NewClientFromBackup() to API Quick Reference

docusaurus-site/docs/quick-reference.md

@@ -112,6 +112,15 @@ func NewClient(ndfJSON, storageDir string, password []byte,
 
 `NewClient` creates client storage, generates keys, connects, and registers with the network. Note that this does not register a username/identity, but merely creates a new cryptographic identity for adding such information at a later date.
 
+### func NewClientFromBackup
+
+```go
+func NewClientFromBackup(ndfJSON, storageDir string, sessionPassword,
+        backupPassphrase []byte, backupFileContents []byte) ([]*id.ID, string, error)
+```
+
+`NewClientFromBackup` constructs a new client from an encrypted backup. The backup is decrypted using the `backupPassphrase`. On successful client creation, the function will return a JSON encoded list of the E2E partners contained in the backup and a json-encoded string containing parameters stored in the backup.
+
 ### func NewPrecannedClient
 
 ```go