docs(samples): Added UpdateTableDescription example.

[ejdarrow]

@stephaniewang526

[codecov]

Codecov Report

Merging #360 into master will increase coverage by 0.21%.
The diff coverage is n/a.

@@ Coverage Diff @@ ## master #360 +/- ## ============================================ + Coverage 77.70% 77.91% +0.21%  - Complexity 1172 1188 +16  ============================================ Files 77 77 Lines 6153 6218 +65 Branches 660 691 +31 ============================================ + Hits 4781 4845 +64  - Misses 1020 1022 +2  + Partials 352 351 -1 

Impacted Files	Coverage Δ	Complexity Δ
...google/cloud/bigquery/ExtractJobConfiguration.java	93.18% <0.00%> (-1.32%)	39.00% <0.00%> (+12.00%)	⬇️
...e/cloud/bigquery/testing/RemoteBigQueryHelper.java	61.40% <0.00%> (-0.42%)	6.00% <0.00%> (ø%)
.../google/cloud/bigquery/spi/v2/HttpBigQueryRpc.java	5.20% <0.00%> (-0.04%)	2.00% <0.00%> (ø%)
...ain/java/com/google/cloud/bigquery/Clustering.java	100.00% <0.00%> (ø)	5.00% <0.00%> (ø%)
...ain/java/com/google/cloud/bigquery/PolicyTags.java	100.00% <0.00%> (ø)	5.00% <0.00%> (ø%)
...java/com/google/cloud/bigquery/BigtableColumn.java	100.00% <0.00%> (ø)	5.00% <0.00%> (ø%)
...java/com/google/cloud/bigquery/TimelineSample.java	100.00% <0.00%> (ø)	5.00% <0.00%> (ø%)
...va/com/google/cloud/bigquery/TimePartitioning.java	100.00% <0.00%> (ø)	7.00% <0.00%> (ø%)
...om/google/cloud/bigquery/ModelTableDefinition.java	100.00% <0.00%> (ø)	4.00% <0.00%> (ø%)
...src/main/java/com/google/cloud/bigquery/Field.java	83.49% <0.00%> (+0.16%)	27.00% <0.00%> (ø%)
... and 16 more

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[stephaniewang526]

in the future, commit msg should be "docs(samples): added UpdateTableDescription.." so that we can pass conventionalcommit check.