[DOC] Update title and description in README

[kaijchen]

What changes were proposed in this pull request?

Add "Apache" in the title and improve the description.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

See https://github.com/kaijchen/incubator-uniffle/tree/readme#apache-uniffle-incubating

[codecov-commenter]

Codecov Report

Merging #94 (ca77f3c) into master (82d1046) will decrease coverage by 0.88%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master      #94      +/-   ##
============================================
- Coverage     56.33%   55.44%   -0.89%     
+ Complexity     1174     1101      -73     
============================================
  Files           149      140       -9     
  Lines          7977     7607     -370     
  Branches        765      735      -30     
============================================
- Hits           4494     4218     -276     
+ Misses         3241     3155      -86     
+ Partials        242      234       -8     

Impacted Files	Coverage Δ
...org/apache/uniffle/server/ShuffleFlushManager.java	76.70% <0.00%> (-1.71%)	⬇️
.../apache/uniffle/coordinator/ClientConfManager.java	91.54% <0.00%> (-1.41%)	⬇️
...org/apache/spark/shuffle/writer/AddBlockEvent.java
...pache/spark/shuffle/writer/WriteBufferManager.java
...org/apache/spark/shuffle/RssSparkShuffleUtils.java
...e/spark/shuffle/reader/RssShuffleDataIterator.java
...che/spark/shuffle/writer/BufferManagerOptions.java
.../java/org/apache/spark/shuffle/RssSparkConfig.java
...ava/org/apache/spark/shuffle/RssShuffleHandle.java
.../org/apache/spark/shuffle/writer/WriterBuffer.java
... and 2 more

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[jerqi]

LGTM

[kaijchen]

Thanks @jerqi for the review.