update doc

Author: azkrishpy

README.md

@@ -50,7 +50,7 @@ The AWS-C-S3 library is an asynchronous AWS S3 client focused on maximizing thro
 
 2. **Maximum Parts Pending Read - `AWS_CRT_S3_MAX_PARTS_PENDING_READ`**
 
-   Controls the maximum number of parts that can be pending read from the input stream during a multipart upload. Higher values may improve upload throughput for large files by allowing more parts to be read in parallel, at the cost of higher memory usage.
+   Controls the maximum number of parts that can be pending read from the input stream during an individual multipart upload. Higher values may improve upload throughput for large files by allowing more parts to be read in parallel, only if the disk read speed can benefit from more concurrent reading of parts.
 
    Example Usage:
 
@@ -63,10 +63,12 @@ The AWS-C-S3 library is an asynchronous AWS S3 client focused on maximizing thro
 
    **Notes**:
    * Only affects multipart uploads. Small files that fit in a single part are not affected.
+   * If there are multiple parallel multipart upload requests, each upload is limited by the value individually (not cumulatively).
    * Setting this too low may introduce delays between reads, as the meta-request waits for the client to schedule more work.
    * Setting this too high may cause a single upload to hog work tokens, starving other concurrent uploads.
    * The value must be a positive integer (1–4294967295). Invalid or zero values are ignored with a warning, and the default is used.
    * The value is read once on first use and cached for the lifetime of the process.
+   * If the network bandwidth of the device is too low, even a higher value of pending read might not be respected due to having maximum allowed requests in flight.
 
 3. **Test Bucket - `CRT_S3_TEST_BUCKET_NAME`**