Add runtimeClassName value to crossplane helm chart docs

[adrienfuss]

Description

Related PR : crossplane/crossplane#6387
Related issue : crossplane/crossplane#6386

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[jbw976]

looks like Vale is unhappy with the spelling of runtimeClassName:

 176:28   error    Spelling check:                 Crossplane.Spelling 
                   "runtimeClassName"?                                 

I think we can add an exception to https://github.com/crossplane/docs/blob/master/utils/vale/styles/Crossplane/allowed-jargon.txt 🙏

[jbw976]

Awesome, thanks for making this docs update to go along with your contribution in crossplane/crossplane#6387! 🎉