chore: add NOTICE file

[simon824]

No description provided.

[codecov]

Codecov Report

Merging #2066 (a87752c) into master (fb48e83) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #2066      +/-   ##
============================================
- Coverage     68.36%   68.34%   -0.02%     
- Complexity      676      979     +303     
============================================
  Files           481      481              
  Lines         39823    39823              
  Branches       5599     5599              
============================================
- Hits          27226    27219       -7     
- Misses         9953     9959       +6     
- Partials       2644     2645       +1     

Impacted Files	Coverage Δ
.../hugegraph/backend/store/rocksdb/RocksDBTable.java	67.11% <0.00%> (-2.02%)	⬇️
...hugegraph/backend/store/raft/rpc/RpcForwarder.java	69.49% <0.00%> (-1.70%)	⬇️
...n/java/org/apache/hugegraph/schema/IndexLabel.java	76.13% <0.00%> (-1.14%)	⬇️
...ugegraph/backend/store/raft/StoreStateMachine.java	64.86% <0.00%> (-0.91%)	⬇️
...g/apache/hugegraph/backend/store/BackendTable.java	84.52% <0.00%> (-0.60%)	⬇️

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[imbajin]

is the right year? merge it first