docs: how the vortex extension version is determined in ddb (#3135)

Author: 0ax1

duckdb-vortex/Makefile

@@ -2,11 +2,19 @@ PROJ_DIR := $(dir $(abspath $(lastword $(MAKEFILE_LIST))))
 
 EXT_NAME=vortex_duckdb
 EXT_CONFIG=${PROJ_DIR}extension_config.cmake
-EXT_FLAGS=-DCMAKE_OSX_DEPLOYMENT_TARGET=12.0 -DOVERRIDE_GIT_DESCRIBE=v1.2.2
+EXT_FLAGS=-DCMAKE_OSX_DEPLOYMENT_TARGET=12.0
 
 export MACOSX_DEPLOYMENT_TARGET=12.0
-export VCPKG_OSX_DEPLOYMENT_TARGET=12.0
+
+# The version of DuckDB and its Vortex extension is either implicitly set by Git tag, e.g. v1.2.2, or commit
+# SHA if the current commit does not have a tag. The implicitly set version can be overridden by defining the
+# `OVERRIDE_GIT_DESCRIBE` environment variable. In context of the DuckDB community extension build, we have to
+# rely on the Git tag, as DuckDB's CI performs a checkout by Git tag. Therefore, the version can't be explicitly
+# set via environment variable for the community extension build.
+
+# export OVERRIDE_GIT_DESCRIBE=v1.2.2
 export VCPKG_FEATURE_FLAGS=-binarycaching
+export VCPKG_OSX_DEPLOYMENT_TARGET=12.0
 export VCPKG_TOOLCHAIN_PATH := ${PROJ_DIR}vcpkg/scripts/buildsystems/vcpkg.cmake
 
 include extension-ci-tools/makefiles/duckdb_extension.Makefile