Update README to describe the limitations of the cURL workaround.
Update README to describe the limitations of the cURL workaround.

unikent/splunk-sdk-php,splunk/splunk-sdk-php,shakeelmohamed/splunk-sdk-php,splunk/splunk-sdk-php,splunk/splunk-sdk-php,unikent/splunk-sdk-php,shakeelmohamed/splunk-sdk-php,shakeelmohamed/splunk-sdk-php,unikent/splunk-sdk-php