new file: source/developping.rst
Moved well formed commit from misc.rst to developping.rst
Moved and improved "empty commit at top"

    - moved from misc.rst to developping.rst
    - added new "orphan" syntax
    - commented and fixed worktree/index cleaning
developping.rst: added "adding a part of a file"
error_fix.rst: new indexing
merge.rst: format fix
misc.rst: format fix.
git_info.rst: added tag info and git describe.
sharing.rst: added sharing tags, and complex tag operations
index.rst: added developing to index.