docs: add disk quota requirement restriction to be much more clear

[allencloud]

Signed-off-by: Allen Sun allensun.shl@alibaba-inc.com

Ⅰ. Describe what this PR did

docs: add disk quota requirement restriction to be much more clear.

Without this pull request, there is no rule for how to setting specific disk quota for container and volume.

The effect taken by disk-quota and quota-id is like the following sheet:

disk-quota	quota-id(<0)	quota-id(=0)	quota-id(>0)
.*=10GB	auto gen quota-id and return，rootfs+n*volume(total 10GB)	no setting quotaID，rootfs 10GB，each volume 10GB	setting as input quota-id, rootfs+n*volume(total 10GB)
/=10GB	auto gen quota-id and return，only rootfs 10GB)	no setting quotaID，only rootfs 10GB	setting as input quota-id, only rootfs 10GB
/=10GB,/a=10GB	invalid	no setting quotaID，rootfs=10GB, only volume mapped to /a 10GB	invalid

Ⅱ. Does this pull request fix one issue?

none

Ⅲ. Why don't you add test cases (unit test/integration test)? (你真的觉得不需要加测试吗？)

doc pr, no test. And for the rules, I think @rudyfly should add more than 10 test cases for the combination of disk-quota and quota-id.

Ⅳ. Describe how to verify it

none

Ⅴ. Special notes for reviews

none

[codecov-io]

Codecov Report

Merging #2142 into master will increase coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2142      +/-   ##
==========================================
+ Coverage   64.38%   64.42%   +0.04%     
==========================================
  Files         209      209              
  Lines       16629    16629              
==========================================
+ Hits        10706    10714       +8     
+ Misses       4592     4589       -3     
+ Partials     1331     1326       -5

Flag	Coverage Δ
#criv1alpha1test	33.03% <ø> (+0.03%)	⬆️
#criv1alpha2test	33.4% <ø> (+0.02%)	⬆️
#integrationtest	39.28% <ø> (-0.04%)	⬇️
#unittest	23.91% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
ctrd/image.go	76.75% <0%> (-0.44%)	⬇️
cri/v1alpha1/cri.go	64.04% <0%> (+0.34%)	⬆️
daemon/mgr/container.go	56.86% <0%> (+0.41%)	⬆️
ctrd/watch.go	80.3% <0%> (+4.54%)	⬆️

[rudyfly]

LGTM