[DOCS] Simplify workflow examply in README.md

[sbuerk]

The README.md contains a GitHub workflow example
for publishing in on pushed tags and extracts from
a annotated tag content created with

git tag -a -m "some content"

filtering the git tag list for the extracted version
and telling to display max 10 lines for the content,
and extracting the tag prefix from the first line
using a sed regexp pattern.

git provides a simpler way using the format option,
which this change adopts in the aforementioned example.

To be precise, following:

git tag -n10 -l ${{ env.version }} | sed "s/^[0-9.]*[ ]*//g"

is replaced with

git tag -l ${{ env.version }} --format '%(contents)'

which displays only the tag content and removes the need
to extract the tag from the first line.