It sounds like you want a story based on the technical process of installing a custom boot image (like boot.img) for crDroid (a popular custom Android ROM).
Unlocked Bootloader: Your device bootloader must be unlocked. crdroid bootimg install
adb sideload custom_boot.img
fastboot set_active other
fastboot flash boot crdroid_boot.img
Once the device is in Fastboot mode (usually a black screen with the Android robot or text), verify your PC can see it: It sounds like you want a story based
Or manually: Power off โ Press Volume Down + Power (varies by device). fastboot set_active other fastboot flash boot crdroid_boot
Now that the boot image (which often contains the recovery environment) is flashed:
#!/system/bin/sh