[r] Update documentation on g++ requirement for R package

[CharlesBordet]

Issue and/or context:

Issue #2029 on updating documentation to mention the version of C++ compiler to install the R package

Changes:

Update aps/r/README.md

Notes for Reviewer:

N/A

[eddelbuettel]

That looks good to me!

Thank you for helping to make our documentation better!

[codecov]

Codecov Report

Merging #2031 (845d678) into main (44bfad4) will decrease coverage by 8.16%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2031      +/-   ##
==========================================
- Coverage   75.87%   67.72%   -8.16%     
==========================================
  Files         136       52      -84     
  Lines       10526     4189    -6337     
  Branches      206        0     -206     
==========================================
- Hits         7987     2837    -5150     
+ Misses       2443     1352    -1091     
+ Partials       96        0      -96     

Flag	Coverage Δ
libtiledbsoma	?
python	?
r	67.72% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
python_api	∅ <ø> (∅)
libtiledbsoma	∅ <ø> (∅)