Fix document in io.md

[ftbabi]

Fix document in io.md
resolve: #798

[codecov]

Codecov Report

Merging #813 (f28d258) into master (93980b4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #813   +/-   ##
=======================================
  Coverage   62.23%   62.23%           
=======================================
  Files         144      144           
  Lines        8506     8506           
  Branches     1522     1522           
=======================================
  Hits         5294     5294           
  Misses       2945     2945           
  Partials      267      267           

Flag	Coverage Δ
unittests	62.23% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 93980b4...ad3e1e3. Read the comment docs.

[ycxioooong]

LGTM

[OpenMMLab-Assistant-007]

Hi!
@ftbabi
First of all, we want to express our gratitude for your significant PR in the OpenMMLab project. Your contribution is highly appreciated, and we are grateful for your efforts in helping improve this open-source project during your personal time. We believe that many developers will benefit from your PR.

We would also like to invite you to join our Special Interest Group (SIG) private channel on Discord, where you can share your experiences, ideas, and build connections with like-minded peers. To join the SIG channel, simply message moderator— OpenMMLab on Discord or briefly share your open-source contributions in the #introductions channel and we will assist you. Look forward to seeing you there! Join us ：https://discord.gg/UjgXkPWNqA

If you have WeChat account，welcome to join our community on WeChat. You can add our assistant ：openmmlabwx. Please add "mmsig + Github ID" as a remark when adding friends：）
Thank you again for your contribution❤