Fixing minor typos in the vtf documentation

[thepith]

Description of changes:

This fixes minor typos in the documentation in the section 14.5. Writing VTF files. The main issue which was fixed is the wrong code in the example.

[codecov]

Codecov Report

Merging #2373 into python will decrease coverage by <1%.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           python   #2373   +/-   ##
======================================
- Coverage      72%     72%   -1%     
======================================
  Files         395     395           
  Lines       18784   18784           
======================================
- Hits        13581   13561   -20     
- Misses       5203    5223   +20

Impacted Files	Coverage Δ
src/core/lattice.cpp	82% <0%> (-7%)	⬇️
src/core/domain_decomposition.cpp	88% <0%> (-4%)	⬇️
src/core/layered.cpp	78% <0%> (-1%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f80bd28...4d5deb0. Read the comment docs.