add code comment for connector

[Nicole00]

No description provided.

[codecov-commenter]

Codecov Report

Merging #32 (9439fee) into master (54bce41) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #32   +/-   ##
=========================================
  Coverage     73.86%   73.86%           
  Complexity      152      152           
=========================================
  Files            24       24           
  Lines          1580     1580           
  Branches        255      255           
=========================================
  Hits           1167     1167           
  Misses          266      266           
  Partials        147      147           

Impacted Files	Coverage Δ
...ala/com/vesoft/nebula/connector/NebulaConfig.scala	78.80% <ø> (ø)
...a/com/vesoft/nebula/connector/PartitionUtils.scala	100.00% <ø> (ø)
...vesoft/nebula/connector/nebula/GraphProvider.scala	52.38% <ø> (ø)
.../vesoft/nebula/connector/nebula/MetaProvider.scala	66.03% <ø> (ø)
...oft/nebula/connector/writer/NebulaEdgeWriter.scala	74.60% <ø> (ø)
...t/nebula/connector/writer/NebulaVertexWriter.scala	70.73% <ø> (ø)

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