Merge branch 'sl/maint-git-svn-docs' into maint

* sl/maint-git-svn-docs:
git-svn: Note about tags.
git-svn: Expand documentation for --follow-parent
git-svn: Recommend use of structure options.
git-svn: Document branches with at-sign(@).

diff --cc Documentation/git-svn.txt
Simple merge