docs: add documentation for git commit hash change detection

AI-Generated: true
AI-Model: claude-3.5-sonnet
Signed-off-by: AtomicFS <vojtech.vesely@9elements.com>

Author: AtomicFS

docs/src/firmware-action/change_detection.md

@@ -38,3 +38,8 @@ On next run, this file (if exists) is loaded with time stamp of last successful
 ## Configuration file changes
 
 Firmware-action can also detect changes in the configuration file. For each module, on each successful build, it stores a copy of the configuration in `.firmware-action/configs/` directory. On next run, current configuration is compared to configuration of last successful build, and if the configuration for the specific module differs, module is re-built.
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+## Git commit hash changes
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+`firmware-action` can detect changes based on git commit hashes. For each module, on each successful build, it stores the git commit hash of the module's repository path (`repo_path`) in `.firmware-action/git-hash/` directory. On next run, the current git commit hash of the module's repository is compared to the stored hash from the last successful build. If the hashes differ, indicating that the module's repository has been changed, the module is re-built.