update instalation instructions in README
update instalation instructions in README

- update versions
- update spack section (SIRIUS is now in the official repo)
- explicitly mention switches to build with optional dependencies

toxa81/sirius,electronic-structure/sirius,electronic-structure/sirius,electronic-structure/sirius,toxa81/sirius,electronic-structure/sirius,electronic-structure/sirius,toxa81/sirius,toxa81/sirius,toxa81/sirius,electronic-structure/sirius,electronic-structure/sirius,toxa81/sirius