add to ~/.bashrc:  Export of $NVM env variable and load nvm command.

def enable_nvm():
    '''add to ~/.bashrc:  Export of $NVM env variable and load nvm command.'''
    bash_snippet = '~/.bashrc_nvm'
    install_file_legacy(path=bash_snippet)
    prefix = flo('if [ -f {bash_snippet} ]; ')
    enabler = flo('if [ -f {bash_snippet} ]; then source {bash_snippet}; fi')
    if env.host == 'localhost':
        uncomment_or_update_or_append_line(filename='~/.bashrc', prefix=prefix,
                                           new_line=enabler)
    else:
        print(cyan('\nappend to ~/.bashrc:\n\n    ') + enabler)