docs: Update secure-boot link in readme

Author: timg236

Readme.md

@@ -184,4 +184,4 @@ Example metadata file contents written to `metadata/SERIAL_NUMBER.json`
 
 <a name="secure-boot"></a>
 ## Secure Boot
-This repository contains the low-level tools and firmware images for enabling secure-boot/verified boot on Compute Module 4 and  Compute Module 5.
+See: [secure-boot](docs/secure-boot.md) reference.

docs/secure-boot.md

@@ -22,8 +22,8 @@ Secure-boot uses cryptographic signing to ensure the OS kernel and all required
 If any signature or hash verification fails, the current boot mode is aborted and the firmware advances to the next boot mode.
 
 See also:-
-* Secure boot BCM2711 [chain of trust diagram](docs/secure-boot-chain-of-trust-2711.pdf).
-* Secure boot BCM2712 [chain of trust diagram](docs/secure-boot-chain-of-trust-2712.pdf).
+* Secure boot BCM2711 [chain of trust diagram](secure-boot-chain-of-trust-2711.pdf).
+* Secure boot BCM2712 [chain of trust diagram](secure-boot-chain-of-trust-2712.pdf).
 
 ## boot.img files
 Secure-boot requires a self-contained ramdisk (`boot.img`) FAT image containing the GPU firmware, kernel and any other dependencies that would normally be loaded from the boot partition.