Use relative links for docs

- Also fix imgtool script link

Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/README.md b/README.md
index 9d99695..4986e7c 100644
--- a/README.md
+++ b/README.md
@@ -41,12 +41,12 @@
 
 For more information in the source, here are some pointers:
 
-- [boot/bootutil](https://github.com/runtimeco/mcuboot/tree/master/boot/bootutil): The core of the bootloader itself.
-- [boot/boot\_serial](https://github.com/runtimeco/mcuboot/tree/master/boot/boot_serial): Support for serial upgrade within the bootloader itself.
-- [boot/zephyr](https://github.com/runtimeco/mcuboot/tree/master/boot/zephyr): Port of the bootloader to Zephyr
-- [boot/mynewt](https://github.com/runtimeco/mcuboot/tree/master/boot/mynewt): Mynewt bootloader app
-- [imgtool](https://github.com/runtimeco/mcuboot/tree/master/imgtool): A tool to securely sign firmware images for booting by mcuboot.
-- [sim](https://github.com/runtimeco/mcuboot/tree/master/sim): A bootloader simulator for testing and regression
+- [boot/bootutil](boot/bootutil): The core of the bootloader itself.
+- [boot/boot\_serial](boot/boot_serial): Support for serial upgrade within the bootloader itself.
+- [boot/zephyr](boot/zephyr): Port of the bootloader to Zephyr
+- [boot/mynewt](boot/mynewt): Mynewt bootloader app
+- [imgtool](scripts/imgtool.py): A tool to securely sign firmware images for booting by mcuboot.
+- [sim](sim): A bootloader simulator for testing and regression
 
 ## Joining