[HapticsDevice] Describe the relationship with the Haptics explainer

[jyasskin]

I followed the link from the WebApps WG charter to https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/HapticsDevice/explainer.md, which hasn't been changed since 2021. @marcoscaceres later informed me that the current version is https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/Haptics/explainer.md. Could you add a pointer?

[marcoscaceres]

I filed a bug to update the WebApps Charter: w3c/webappswg#144

Microsoft folks, can you confirm that's ok.