doc: Correct info on code_location parameter (#1129)

Corrected info on resulting S3 path if code_location is specified and added warning about trailing slash

Author: zaeemnalla

src/sagemaker/estimator.py

@@ -1280,11 +1280,10 @@ def __init__(
                 (default: logging.INFO). Valid values are defined in the Python
                 logging module.
             code_location (str): The S3 prefix URI where custom code will be
-                uploaded (default: None). The code file uploaded in S3 is
-                'code_location/source/sourcedir.tar.gz'. If not specified, the
-                default code location is s3://default_bucket/job-name/. And code
-                file uploaded to S3 is
-                s3://default_bucket/job-name/source/sourcedir.tar.gz
+                uploaded (default: None) - don't include a trailing slash since
+                a string prepended with a "/" is appended to ``code_location``. The code
+                file uploaded to S3 is 'code_location/job-name/source/sourcedir.tar.gz'.
+                If not specified, the default ``code location`` is s3://default_bucket/job-name/.
             image_name (str): An alternate image name to use instead of the
                 official Sagemaker image for the framework. This is useful to
                 run one of the Sagemaker supported frameworks with an image