Add Switch-Wire wiring diagram for SKR mini E3 V3.0 board

[GadgetAngel]

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*updated Electrical Index.md file to add the Switch-Wire SKR mini E3 V3.0. *added initial preparation diagram *added description for wiring diagram *added wiring diagram for Voron Switch-wire *added Color Pin diagram for Bigtreetech SKR mini E3 V3.0 *added URL to the original Bigtreetech Github Repo on the SKR mini E3 V3.0 board