improve doc on how to add plugin

Signed-off-by: Édouard Lopez <dev+github@edouard-lopez.com>
update aliases

Signed-off-by: Édouard Lopez <dev+github@edouard-lopez.com>
[readme] update intro

Signed-off-by: Édouard Lopez <dev+github@edouard-lopez.com>
[readme] splitting 'install & configuration' section

Signed-off-by: Édouard Lopez <dev+github@edouard-lopez.com>
[readme] add `yo` completion section

Signed-off-by: Édouard Lopez <dev+github@edouard-lopez.com>
[readme] add `bower` completion section

Signed-off-by: Édouard Lopez <dev+github@edouard-lopez.com>
[readme] add `grunt` completion section

Signed-off-by: Édouard Lopez <dev+github@edouard-lopez.com>
update aliases section

Signed-off-by: Édouard Lopez <dev+github@edouard-lopez.com>