[docs] Add Conan usage on README

[uilianries]

• Add a new installation step in README file, explaining how to use Conan to install glog.

[codecov-commenter]

Codecov Report

Merging #862 (40c312e) into master (b70ea80) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #862   +/-   ##
=======================================
  Coverage   73.29%   73.29%           
=======================================
  Files          17       17           
  Lines        3292     3292           
=======================================
  Hits         2413     2413           
  Misses        879      879           

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[sergiud]

Thanks!