[BUGFIX] Fixing broken logo for legacy RTD docs

[kyleaton]

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Changes proposed in this pull request:
-Add logo and fix location

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[kyleaton]

This PR address #3613

[kyleaton]

I previewed the build and it seems to be working fine but I'm a little skeptical the issue may still exist when it goes live due to the domain change... I'll keep an eye on it and if it doesn't work I'll point to a logo hosted elsewhere

[austiezr]

LGTM!