docs: document Support for gorm

[olavloite]

Add documentation to indicate Support for gorm.

[codecov]

Codecov Report

Merging #469 (c0a6f04) into postgresql-dialect (6ef7240) will increase coverage by 1.69%.
The diff coverage is 96.58%.

❗ Current head c0a6f04 differs from pull request most recent head 7da278c. Consider uploading reports for the commit 7da278c to get more accurate results

@@                   Coverage Diff                    @@
##             postgresql-dialect     #469      +/-   ##
========================================================
+ Coverage                 86.32%   88.02%   +1.69%     
- Complexity                 1914     2053     +139     
========================================================
  Files                       122      122              
  Lines                      6216     6779     +563     
  Branches                    849      955     +106     
========================================================
+ Hits                       5366     5967     +601     
+ Misses                      605      578      -27     
+ Partials                    245      234      -11     

Flag	Coverage Δ
all_tests	88.02% <96.58%> (+1.69%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ud/spanner/pgadapter/utils/ClientAutoDetector.java	93.18% <ø> (ø)
...e/cloud/spanner/pgadapter/utils/PgJdbcCatalog.java	0.00% <ø> (ø)
.../cloud/spanner/pgadapter/utils/MutationWriter.java	92.09% <69.23%> (+1.70%)	⬆️
...gle/cloud/spanner/pgadapter/error/PGException.java	90.62% <85.71%> (+0.96%)	⬆️
...panner/pgadapter/wireprotocol/DescribeMessage.java	85.50% <88.88%> (-0.61%)	⬇️
...oud/spanner/pgadapter/parsers/TimestampParser.java	91.78% <90.90%> (-1.44%)	⬇️
...oud/spanner/pgadapter/statements/SimpleParser.java	91.98% <91.57%> (+0.64%)	⬆️
...ud/spanner/pgadapter/wireprotocol/BindMessage.java	82.97% <93.33%> (+0.47%)	⬆️
...pter/statements/IntermediatePreparedStatement.java	94.82% <94.23%> (+7.61%)	⬆️
...le/cloud/spanner/pgadapter/parsers/UuidParser.java	95.34% <95.34%> (ø)
... and 59 more

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