Update customizing.md (#5328)
Update customizing.md (#5328)

* Fix links for stacks

Signed-off-by: Stevan Le Meur <82bfe19b0c71b819e93a6ce8848c5385b08dbc48@gmail.com>

* Update links on various entry point to the documentation

Signed-off-by: Stevan Le Meur <82bfe19b0c71b819e93a6ce8848c5385b08dbc48@gmail.com>

* Create CUSTOMIZING.md

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