boards: reel_board: update docu for the first board release

[jfischer-no]

Update images and connection tables for the first board release.

[codecov-io]

Codecov Report

Merging #10694 into master will decrease coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #10694      +/-   ##
==========================================
- Coverage   53.24%   53.08%   -0.16%     
==========================================
  Files         214      214              
  Lines       25828    25828              
  Branches     5695     5695              
==========================================
- Hits        13753    13712      -41     
- Misses       9760     9807      +47     
+ Partials     2315     2309       -6

Impacted Files	Coverage Δ
include/posix/posix_sched.h	0% <0%> (-100%)	⬇️
lib/posix/pthread_barrier.c	0% <0%> (-100%)	⬇️
lib/posix/pthread_cond.c	62.5% <0%> (-20.84%)	⬇️
lib/posix/pthread.c	68.03% <0%> (-12.33%)	⬇️
lib/posix/pthread_mutex.c	76.38% <0%> (-1.39%)	⬇️
lib/posix/pthread_sched.c	62.5% <0%> (+20.83%)	⬆️

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[dbkinder]

LGTM, thanks.