add Supplementary Figure 6 caption

assays/AbsorptionSpectraAndODMeasurements/README.md

@@ -15,4 +15,14 @@ Average values from three biological replicates, error bars represent the standa
 
 ### Supplementary Figure 5 source
 
-https://www.frontiersin.org/articles/10.3389/fpls.2023.1024981/full#supplementary-material
\ No newline at end of file
+https://www.frontiersin.org/articles/10.3389/fpls.2023.1024981/full#supplementary-material
+
+### Supplementary Figure 6 caption
+
+**Supplementary Figure 6:** Spectra of *Synechocystis* cells after 3 days incubation with 5 mM
+rhamnose, measured in 1 cm cuvettes. OD750 values were equalized across all measurements in the
+cuvettes, then the spectra were baseline corrected by subtracting the OD750 value.
+
+### Supplementary Figure 6 source
+
+https://www.frontiersin.org/articles/10.3389/fpls.2023.1024981/full#supplementary-material