update README.md

## IMPORTANT

**The name of the file**

`Problem_subquestion_others`, like `P1_5_a1.m`, and set the name of the photos with `filename_photoname.png`

**The files in this project should follow the following instructions.**

### The name of the file

`Problem_subquestion_others.m`, like `P1_5_a1.m`, and set the name of the photos with `filename_photoname_out/photoindex.png`like `P_1_5_a1_out1.png`

### The part contained in the code

1. The code implementation

2. Plot

3. save the plots by function `saveas();`

## Introduction

**LAB1 should be submitted before 4th March**

In lab 1

## Lab 2: Linear Time-Invariant Systems

## Lab 3: Fourier Series Representation of Periodic Signals