Create README.md

README.md

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+You can generate `Totp` code based on time, `UserSecurityStamp` and `UserIdentifier`
+**Usage**
+```CSharp
+public async ValueTask<int> GetTwoFactorTotpCode(string email)
+{
+    var user = await GetUserByEmail(email);
+
+    var modifier = GetModifier(user, TotpEnum.TwoFactor);
+
+    var totpCode = TotpService.GenerateCode(user.SecurityStamp.ToString(), modifier);
+
+    return totpCode;
+}
+
+public async ValueTask<bool> ValidateTwoFactorTotpCode(string email, int totpCode)
+{
+    var user = await GetUserByEmail(email);
+
+    string modifier = GetModifier(user, TotpEnum.TwoFactor);
+
+    var isValid = TotpService.ValidateCode(
+        user.SecurityStamp.ToString(), 
+        totpCode, 
+        modifier, 
+        _userOption.TwoFactorTotpExpiration);
+
+    return isValid;
+}
+
+private static string GetModifier(User user, TotpEnum totpEnum)
+{
+    return $"Totp:{user.Id}:{totpEnum}";
+}
+```
+TotpEnum:
+```CSharp
+public enum TotpEnum : byte
+{
+    TwoFactor = 1,
+    Activation = 2,
+    Deactivation = 4
+}
+
+```