Restore the axes of the Venus phosphine figure on deck 6

The figure was a dark-mode screenshot with the axis labels and units cut off. The deck now shows row D of Figure 3 of Lincowski et al. (2021), extracted from the published PDF, with the velocity, frequency, line contrast and brightness temperature axes, and the caption names the panels and the source figure.

Author: timlichtenberg

book/_static/slides/lecture06.pdf

@@ -426,7 +426,7 @@ \section{Recent advances \& outlook}
 
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-  \ipshero{lincowski2021_phosphine_so2}{The reported 267~GHz Venus phosphine feature is fit by mesospheric $\mathrm{SO_2}$, a controversy that NASA's DAVINCI probe will test in situ. Lincowski et al.\ (2021).}
+  \ipshero{lincowski2021_phosphine_so2}{The reported 267~GHz Venus phosphine feature (left: line contrast against Doppler velocity, JCMT data in orange) is fit by mesospheric $\mathrm{SO_2}$ (right: line contrast and brightness temperature against frequency, molecular line positions below), a controversy that NASA's DAVINCI probe will test in situ. Reproduced from Lincowski et al.\ (2021), Fig.\ 3D.}
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