Update README for llvm_autotuning

[lqwk]

To specify custom log directories for llvm_autotuning.info I think we need to explicitly spell out the option --log-dirs, otherwise it doesn't work.

[codecov-commenter]

Codecov Report

Merging #740 (d5a28db) into development (1368383) will decrease coverage by 0.03%. The diff coverage is n/a.

@@               Coverage Diff               @@
##           development     #740      +/-   ##
===============================================
- Coverage        88.83%   88.79%   -0.04%     
===============================================
  Files              129      129              
  Lines             7854     7854              
===============================================
- Hits              6977     6974       -3     
- Misses             877      880       +3     

Impacted Files	Coverage Δ
compiler_gym/envs/llvm/datasets/cbench.py	79.49% <0.00%> (-1.08%)	:arrow_down:

[ChrisCummins]

LGTM, thanks!