[MRG+1] Improve docs of S3 Storage to make Python version more explicit #3294
The documentation of the S3 storage backend (https://doc.scrapy.org/en/latest/topics/feed-exports.html#s3) suggest the use of the libraries botocore (https://github.com/boto/botocore) or boto (https://github.com/boto/boto). However, boto library will work only if the user is using Python 2 (as it is correctly explained here https://doc.scrapy.org/en/latest/topics/feed-exports.html#storages).
Besides the fact of this information is there, I believe that it would be better for the user reading the documentation to have this note also inside the specific section of S3 storage backend.
When issue #1866 is resolved, this could be removed anyway.
@@ Coverage Diff @@ ## master #3294 +/- ## ======================================= Coverage 82.14% 82.14% ======================================= Files 228 228 Lines 9599 9599 Branches 1385 1385 ======================================= Hits 7885 7885 Misses 1456 1456 Partials 258 258