Fix internal links

doc/manual/src/advanced-topics/distributed-builds.md

doc/manual/src/advanced-topics/post-build-hook.md

doc/manual/src/command-ref/conf-file.md

doc/manual/src/command-ref/env-common.md

doc/manual/src/command-ref/nix-build.md

doc/manual/src/command-ref/nix-collect-garbage.md

doc/manual/src/command-ref/nix-env.md

doc/manual/src/command-ref/nix-hash.md

doc/manual/src/command-ref/nix-instantiate.md

doc/manual/src/command-ref/nix-store.md

doc/manual/src/command-ref/opt-common.md

doc/manual/src/expressions/advanced-attributes.md

doc/manual/src/expressions/builtins.md

doc/manual/src/expressions/simple-building-testing.md

doc/manual/src/installation/installing-binary.md

doc/manual/src/installation/multi-user.md

doc/manual/src/package-management/basic-package-mgmt.md

doc/manual/src/package-management/channels.md

doc/manual/src/package-management/s3-substituter.md

doc/manual/src/release-notes/rl-2.0.md