capitalize words for heading in regridding doc

[zfan001]

Description:
Every significant word in headings of the regridding document should be capitalized. Just a minor fixing for consistence with the documentation style.

Testing:

• [Y] Ran tests and they passed OK

[codecov]

Codecov Report

Merging #1519 (0408573) into master (42aaa60) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1519   +/-   ##
=======================================
  Coverage   97.86%   97.87%           
=======================================
  Files         108      108           
  Lines        9387     9395    +8     
=======================================
+ Hits         9187     9195    +8     
  Misses        200      200           

Impacted Files	Coverage Δ
improver/developer_tools/metadata_interpreter.py	98.24% <0.00%> (+0.05%)	⬆️

---

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 42aaa60...0408573. Read the comment docs.

[tjtg]

Minor documentation change, all looks OK.