Fix markdown list in installation.md (#56165)
Documenter.jl requires all trailing list content to follow the same
indentation as the header. So, in the current view
(https://docs.julialang.org/en/v1/manual/installation/#Command-line-arguments)
the list appears broken.
(cherry picked from commit 9f92989274640b14d4d0015107e501e7252344b2)