Update README.md (#1282)

Added info for DEPTHAI_PROFILING env variable.

Author: jakaskerl

README.md

@@ -205,6 +205,7 @@ The following environment variables can be set to alter default behavior of the
 | DEPTHAI_CRASHDUMP_TIMEOUT | Specifies the duration in seconds to wait for device reboot when obtaining a crash dump. Crash dump retrieval disabled if 0. |
 | DEPTHAI_ENABLE_ANALYTICS_COLLECTION | Enables automatic analytics collection (pipeline schemas) used to improve the library |
 | DEPTHAI_DISABLE_CRASHDUMP_COLLECTION | Disables automatic crash dump collection used to improve the library |
+| DEPTHAI_PROFILING | Enables runtime profiling of data transfer between the host and connected devices. Set to 1 to enable. Requires DEPTHAI_LEVEL=debug or lower to print. |
 
 ## Running tests