[#552] docs: add more doc about spark.serializer requirement

[advancedxy]

What changes were proposed in this pull request?

add more doc and warning

Why are the changes needed?

Fixes #552

Does this PR introduce any user-facing change?

No

How was this patch tested?

No need.

[codecov-commenter]

Codecov Report

Merging #556 (45c0b9a) into master (ebbe2db) will increase coverage by 0.64%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #556      +/-   ##
============================================
+ Coverage     60.21%   60.85%   +0.64%     
- Complexity     1784     1795      +11     
============================================
  Files           205      213       +8     
  Lines         11557    12372     +815     
  Branches       1042     1050       +8     
============================================
+ Hits           6959     7529     +570     
- Misses         4190     4435     +245     
  Partials        408      408              

Impacted Files	Coverage Δ
...he/uniffle/client/impl/ShuffleWriteClientImpl.java	34.44% <0.00%> (-0.51%)	⬇️
.../java/org/apache/uniffle/common/util/RssUtils.java	58.45% <0.00%> (ø)
...a/org/apache/uniffle/common/ShuffleServerInfo.java	75.00% <0.00%> (ø)
.../org/apache/uniffle/server/ShuffleTaskManager.java	76.76% <0.00%> (ø)
...pache/uniffle/server/ShuffleServerGrpcMetrics.java	100.00% <0.00%> (ø)
.../apache/uniffle/coordinator/ClientConfManager.java	92.95% <0.00%> (ø)
...fle/coordinator/metric/CoordinatorGrpcMetrics.java	100.00% <0.00%> (ø)
...inator/access/checker/AccessCandidatesChecker.java	85.50% <0.00%> (ø)
...ain/java/org/apache/uniffle/server/StatusCode.java
...eploy/kubernetes/operator/pkg/utils/coordinator.go	0.00% <0.00%> (ø)
... and 18 more

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[kaijchen]

Hi @advancedxy, I think the PR title needs to be changed, obviously this is not a chore.
If there is no production code change, I would say this is a docs PR.

[advancedxy]

Hi @advancedxy, I think the PR title needs to be changed, obviously this is not a chore. If there is no production code change, I would say this is a docs PR.

It also involves code change, so I choose chore over docs. But docs or chore are both fine for me.

[kaijchen]

It also involves code change, so I choose chore over docs. But docs or chore are both fine for me.

chore is not OK, it's only for things like CI, dependencies, etc.

[advancedxy]

It also involves code change, so I choose chore over docs. But docs or chore are both fine for me.

chore is not OK, it's only for things like CI, dependencies, etc.

In my opinion, anything trivial enough could go to the chore category. It doesn't strictly bind to build stuff.

[advancedxy]

ping @jerqi

[roryqi]

LGTM, thanks @advancedxy @kaijchen