Add comprehensive help documentation including:
- Introduction and overview
- Usage of :Licenser command
- Configuration options (g:licenser_author)
- Complete list of supported filetypes
- Complete list of supported licenses
- Usage examples
Documentation follows standard Vim help format and can be
accessed with :help licenser once the plugin is installed.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
