CONFIG_IS_BOOTLOADER is poorly named and documented

[SebastianBoe]

See mcu-tools/mcuboot#230 for details

[nashif]

put MCUBOOT aside, you can build zephyr to act as a bootloader, so there is nothing confusing here

This option indicates that Zephyr will act as a bootloader to execute
a separate Zephyr image payload.

Not sure how this can be written in some other way, IMO it is clear enough.

[SebastianBoe]

Perhaps:

This option will offset the ORIGIN of the MEMORY region SRAM by "CONFIG_BOOTLOADER_SRAM_SIZE" kB and reduce it's SIZE by the same amount.