README: clarification on kernel requirements for I/O

[dilyanpalauzov]

After reducing the kernel features, I found that htop showed for DISK R/W, DISK READ, DISK WRITE N/A. Then I figured out when the file /proc/$PID/task/$PID/io was maintained and here comes the outcome.

[natoscott]

This relates to Linux specifically, so please move this 5 lines down from where you have it (into the markdown section with "Linux" header). There's no need for the comma in your sentence there either.

[natoscott]

LGTM, thanks.