update docs

Signed-off-by: NAnnie_wang <annie.wangli@huawei.com>

en/device-dev/faqs/faqs-environment-setup.md

@@ -88,8 +88,6 @@
      python3 -m pip install -i https://pypi.tuna.tsinghua.edu.cn/simple ohos-build
      ```
 
-     
-
 ### Python 3 Installation
 
 #### "configure: error: no acceptable C compiler found in $PATH"
@@ -109,9 +107,8 @@
 - **Solution**
 
   1. Run the **apt-get install gcc** command to install GCC online.
-  2. Install Python 3.
-
 
+  2. Install Python 3.
 
 
 #### "-bash: make: command not found"
@@ -135,8 +132,6 @@
   2. Install Python 3.
 
 
-
-
 #### "zlib not available"
 
 - **Symptom**
@@ -240,3 +235,43 @@
   sudo apt-get remove  python3-apt
   sudo apt-get install python3-apt
   ```
+
+### Updating Source Code
+- **Scenario**
+
+  Update the OpenHarmony source code downloaded to the branch (for example, Master) source code.
+
+- **Solution**
+
+  1. Go to the OpenHarmony root directory.
+  
+     Check that the root directory has a **.repo** folder, which is usually hidden. If the **.repo** folder does not exist, decompress the obtained source code package again to obtain complete source code.
+  
+  2. Run the **repo init** command to initialize the source code repository information.
+
+     In the command, *branch* indicates the branch name, for example, **master** or **OpenHarmony-3.2-Beta3**.
+     ```shell
+     repo init -u https://gitee.com/openharmony/manifest -b branch --no-repo-verify
+     ```
+
+  3. Download and update the source code file.
+
+     ```shell
+     repo sync -c
+     repo forall -c 'pwd;git lfs pull'
+     ```
+     To keep the working directory clean, run the following command:
+  
+     >![icon-note.gif](public_sys-resources/icon-caution.gif) **CAUTION**<br>
+     >This command will reset the local workspace and delete files or directories that are not managed by gitee. Exercise caution when performing this operation.
+     ```shell
+     repo forall -c 'git reset --hard;git clean -fdx'
+     ```
+
+  4. Run the prebuilts script to install the compiler and binary tool.
+
+     ```shell
+     bash build/prebuilts_download.sh
+     ```
+  
+