add checksum verification

Guides/LineageOsInstallation.md

@@ -28,50 +28,67 @@ For overwriting your fairphones boot-loader we will need connection to your pc.
    <SerialNumberOfYourPhone>	device
    ```
 
-## 4. Install LinegaeOS recovery image
+## 4. Prepare recovery image installation
 
-If this step goes wrong your fairphone may remain broken. So be shure, your phone has at least 50% battery.
+The next step is the critical one. If this step goes wrong your fairphone may remain broken. Time to do some checks:
+
+1. Check that your phone has at least 50% battery.
 1. Reboot your fairphone to bootloader mode: Type `adb reboot bootloader` on your computer.
 1. Fairphone should show the bootloader screen.  
 1. Type `fastboot devices` on your computer. The result should show something like
    ```
    <SerialNumberOfYourPhone>	fastboot
    ```
+1. Check whether your downloaded recovery image is not broken. In case of
+   1. windows type `Get-FileHash <image_filename.img>` on your computer.
+   1. linux type `sha256sum <image_filename.img>` on your computer. 
+1. The result should look like   
+   ```
+   b6494278d0a399547a9344a6018a30b388f71a97ef52989bcdd661002f3a8631  lineage-18.1-20210906-recovery-FP3.img
+   ```
+1. Now compare some random parts of the number to the one given on the recovery image download page. Ensure, you are browsing secure with "https".   
+[<img src="img/sha256.png" width="500" height="250">](img/sha256.png)
+
+## 5. Install LinegaeOS recovery image
+
+All checks passed? Then lets do the work:
 1. Type on your computer `fastboot oem unlock`.
 1. Install fastboot image by typing `fastboot flash recovery <image_filename.img>` on your computer (<image_filename.img> is the img-file you have downloaded in 1.).
 1. Type on your computer `fastboot oem lock`.
 
-OEM unlocking / locking will erase all data, so we should ensure to do the lock again.
+OEM unlocking / locking will erase all data, so we should ensure to do the lock again now.
 
-## 5. Install LineageOS
+## 6. Install LineageOS
 
 This step is no more dangerous. You can retry as often you want to. The LineageOs boot-loader will verify your binaries.
 1. Reboot your fairphone again to bootloader mode: Type `adb reboot bootloader` on your computer.
-1. Your fairphone now boots to the new LineageOS recovery image. Then start the recovery mode.   
+2. Your fairphone now boots to the new LineageOS recovery image. Then start the recovery mode.   
 [<img src="img/start.jpg" width="300" height="400">](img/start.jpg)[<img src="img/recovery.jpg" width="300" height="400">](img/recovery.jpg)
 
-1. Choose Factory Reset - Format Data/Factory Reset  
+3. Choose Factory Reset - Format Data/Factory Reset  
 [<img src="img/reset.jpg" width="300" height="400">](img/reset.jpg)[<img src="img/format.jpg" width="300" height="400">](img/format.jpg)
-1. Return to main menu
-1. Apply update - Apply from ADB  
+4. Return to main menu
+5. Apply update - Apply from ADB  
 [<img src="img/apply.jpg" width="300" height="400">](img/apply.jpg)[<img src="img/sideload.jpg" width="300" height="400">](img/sideload.jpg)
-1. Type `adb sideload <lineagos.zip>` on your computer (<lineagos.zip> is the zip-file you have downloaded in 1.).  
+6. Type `adb sideload <lineagos.zip>` on your computer (<lineagos.zip> is the zip-file you have downloaded in 1.).  
 [<img src="img/done.jpg" width="300" height="400">](img/done.jpg)  
 
-### 5.1 Optional installation of Google Apps
+7. Check whether you see the `Step 2/2` on the bottom of your fairphone.
+
+### 6.1 Optional installation of Google Apps
 
 If you can't abstain from the Google Apps or the Google Play Store there exist packages with various scopes, you will find a package comparison here: [https://github.com/opengapps/opengapps/wiki/Package-Comparison](https://github.com/opengapps/opengapps/wiki/Package-Comparison). You have to install Google Aps in front of first the first start wizzard.
 1. Download the favored version from [here](https://opengapps.org/).
 1. Install the gapps the same way, you installed LineageOs: `adb sideload <gapps.zip>`
 
-## 6. Start LineageOS
+## 7. Start LineageOS
 
 First start of your new LineageOS - hurray.
 1. Return to main menu
 1. Choose Reboot system, then your phone should start with the new LineageOS.
 1. Walk through the initial LineageOS setup.
 
-## 7. Download the F-Droid App-Store
+## 8. Download the F-Droid App-Store
 
 For installing more software we recommend F-Droid 
 1. Use the browser on your Fairphone to download F-Droid: [https://www.f-droid.org/](https://www.f-droid.org/)