[RFA:] Update docs about ld -r format restrictions

[Nick Clifton]

Hi Hans-Peter,

> ld:
> 	* ld.texinfo (Options) <-r>: Mention restrictions when using
> 	different object formats.
> 
> bfd/doc:
> 	* bfdint.texi (BFD relocation functions) <different formats>:
> 	Mention that the GNU linker is aware of input-output format
> 	restrictions when generating relocatable output.  Make new
> 	paragraph for final-link case.

Approved.

> BTW, I really think bfdint.texi deserves to be built and installed
> by default; it shouldn't be hidden the way it is now.

Isn't it rather sparse and poorly maintained ?

Cheers
        Nick