Update mconfig.Darwin

[aidan-gibson]

Solves #266
/sbin and /usr/share/man are protected by SIP

[mobin-2008]

Looks good except I have question about /var/run/

[davmac314]

Sorry for being unable to review this myself earlier. I think this change should not have gone through, for the following reasons:

• the default build configuration is provided with the assumption of installing Dinit as a "system" init. For most systems other than (some) Linux systems this is not really feasible but it's nevertheless the default. It can be overridden for all systems via setting appropriate variables (SBINDIR=...) on the command line when doing the build (and make install step).
• SIP, which prevents the default from working at all on MacOS, can be disabled in order to install software in the "protected" directories, and it's reasonable to think that if someone wanted a "system" install of Dinit that they would do this.
• The change affects the "Darwin" configuration, which affects not just MacOS but also other systems based on Darwin, such as PureDarwin (which does not have SIP).

I think all that was really needed was to adjust the build instructions to make it more clear that SBINDIR will often need to be specified (perhaps even with specific mention of SIP). With that in mind, I'm going to revert this change and apply an appropriate documentation change in its place.

Apologies @aidan-gibson for the hassle. I'm assuming this won't affect homebrew installs at all. If you think what I've proposed really is the wrong solution then feel free to post here. Unfortunately your PR was merged before the usual review, which shouldn't have happened.

@mobin-2008 Please don't merge PRs before we have discussed them, in future. I value your input and your reviews but this is my project and I maintain full responsibility for it, which also means I must be the final arbiter and in this case as I have outlined, I do not agree that this should have been merged.