Address issues in `hyperSpec.Rmd`

[GegznaV]

Warnings while building hyperSpec.Rmd:

Rebuilding hyperSpec.Rmd
[WARNING] Citeproc: citation da not found
Warning messages:
1: The label(s) sec:wavel-axis-conv not found 
2: The label(s) sec:square-brack-replace, sec:accessing-extra-data not found 
3: The label(s) sec:square-brack-replace, sec:accessing-extra-data not found 
4: The label(s) fig:paracetamol not found 
5: The label(s) sec:wavelength-indices not found 
6: The label(s) sec:conv-matrix not found 
7: The label(s) sec:wavelength-axis not found 
8: The label(s) fig:fit-shift not found 

Checklist:

• [x] 1: The label(s) sec:wavel-axis-conv not found
• [x] 2: The label(s) sec:square-brack-replace, sec:accessing-extra-data not found
• [x] 3: The label(s) sec:square-brack-replace, sec:accessing-extra-data not found
• [x] 4: The label(s) fig:paracetamol not found
• [x] 5: The label(s) sec:wavelength-indices not found
• [x] 6: The label(s) sec:conv-matrix not found
• [x] 7: The label(s) sec:wavelength-axis not found
• [ ] 8: The label(s) fig:fit-shift not found