bitbake-user-manual: npm fetcher: improve description of SRC_URI format
    
    Using the term "Parameter" which is consistent with the
    description of SRC_URI parameters in the following text.
    
    Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
    Reported-by: Quentin Schulz <foss@0leil.net>
    Reviewed-by: Quentin Schulz <foss+yocto@0leil.net>
    Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>