[DOCFIX] Update project Readme
[DOCFIX] Update project Readme

### What changes are proposed in this pull request?

Update Readme

### Why are the changes needed?

Various minor tunings on readme file

### Does this PR introduce any user facing changes?

None

pr-link: Alluxio/alluxio#13783
change-id: cid-f52f0d6d88e96507dc8252c70cd6f9d03d3c62f7
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