Improve frontend configuration parameters documentation

[paskal]

Variables were documented in the documentation but not in the code, and max_last_comments needed to be documented.

Resolved #764.

[codecov]

Codecov Report

Base: 58.05% // Head: 58.05% // No change to project coverage 👍

Coverage data is based on head (3534e87) compared to base (82f27e6).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1571   +/-   ##
=======================================
  Coverage   58.05%   58.05%           
=======================================
  Files         131      131           
  Lines        2911     2911           
  Branches      736      736           
=======================================
  Hits         1690     1690           
  Misses       1090     1090           
  Partials      131      131           

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[github-actions]

size-limit report 📦

Path	Size
public/embed.mjs	2.03 KB (0%)
public/remark.mjs	72.76 KB (0%)
public/remark.css	8.12 KB (0%)
public/last-comments.mjs	35.67 KB (0%)
public/last-comments.css	3.72 KB (0%)
public/deleteme.mjs	12.05 KB (0%)
public/counter.mjs	749 B (0%)