Doc: Add compressed files notice to README.apache.md

Add a section to README.apache.md listing compressed files present in
the source tree. These files are archives of text files used for
testing purposes and do not contain binary executables.

This clarification is added to comply with Apache release policies
regarding compressed files in source distributions.

See: https://lists.apache.org/thread/zcb0xcxxl28ckqqj24r68jnr7g7t52kx

Author: tuhaihe

README.apache.md

@@ -38,3 +38,15 @@ The following entities have contributed to the Greenplum-based source code under
 - Broadcom Inc.
 
 RAT matchers are used to classify their license headers accordingly.
+
+## Compressed Files in Source
+
+The following compressed files are included in the source tree. These files are archives of text files used for testing purposes and do not contain binary executables. They are not used during the build process.
+
+- contrib/formatter_fixedwidth/data/fixedwidth_small_correct.tbl.gz
+- gpMgmt/demo/gppkg/sample-sources.tar.gz
+- src/bin/gpfdist/regress/data/exttab1/nation.tbl.gz
+- src/bin/gpfdist/regress/data/gpfdist2/gz_multi_chunk.tbl.gz
+- src/bin/gpfdist/regress/data/gpfdist2/gz_multi_chunk_2.tbl.gz
+- src/bin/gpfdist/regress/data/gpfdist2/lineitem.tbl.bz2
+- src/bin/gpfdist/regress/data/gpfdist2/lineitem.tbl.gz