[lld] [lld][docs] Document two linker-script related options for lld ELF (PR #166313)

[Mingming Liu via llvm-commits]

mingmingl-llvm wrote:

> -T is the short alias for --script, and -dT is the short alias for --default-script

Indeed. I think 'setting options under the hood' can be confusing and alias is accurate (per https://github.com/llvm/llvm-project/blob/a55221da6047dace6ec7f24967ce0113429d093f/lld/ELF/Options.td#L601 and https://github.com/llvm/llvm-project/blob/a55221da6047dace6ec7f24967ce0113429d093f/lld/ELF/Options.td#L628). Applied the suggestions.

https://github.com/llvm/llvm-project/pull/166313