Update README / merge Python requirements

README.md

@@ -1,11 +1,22 @@
 # boot4u
 U-Boot loader for PW-x1
 
+# Preparation
+
+1. Install requirements
+
+   ```shellsession
+   $ apt install gcc-arm-linux-gnueabihf
+   $ pip3 install -r requirements.txt
+   ```
+
+2. Put image.jpg in this directory
+
+   - The size must be 480x854 (rotate the picture 90 deg clockwise)
+
 # Build
 
 ```sh
-apt install gcc-arm-linux-gnueabihf
-pip3 install pyelftools
 make
 ```
 

requirements.txt

@@ -1 +1,2 @@
+pyelftools
 pillow