Add more docs for Feature Layer

not complete, but progress..

docs/features/people/household/index.rst

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+
+Household / Shared Accounts
+===========================
+
+A common scenario is where a Customer (or Employee, or Member) is able
+to "share" benefits of their account, with their immediate household.
+There may be other variations but we'll stick with that example here.
+
+Although to clarify, while many e.g. retail food co-ops may consider
+the "Household" concept to be an extension of a "Member" account
+specifically, Rattail instead considers it a logical extension of the
+"Customer" account.  This is because the benefits which are extended
+to the household normally apply to "shopping" specifically, and
+Rattail uses the "Customer" concept to represent that.  (Same holds
+true for a more traditional retailer which might extend benefits to
+the Household of an Employee - the Household will still fall under a
+Customer account logically.)
+
+So it might be possible for Rattail to add a broader / more generic
+"Household" concept later, but for now it's all about Customers.  (And
+a Member account is normally tied to a Customer account, so it's not
+much more than a difference of semantics.)
+
+Okay! With that out of the way...
+
+Household accounts can be tricky.  For instance are these people
+actually tracked in your system?  (Do they need to be?)  If so are
+they tracked as separate accounts or just minimal (e.g. name) info
+somehow tacked onto the main account?  In particular how are the
+accounts represented in your POS system?
+
+Rattail can be used to help track e.g. Household-related links between
+various Person and/or Customer records.  What you do with such links
+is up to you of course, but some ideas:
+
+If your POS allows for it, you might have Rattail keep the POS in sync
+for (at least certain types of) changes to Household-related accounts.
+For instance in the dynamic coupon scenario, let's say you do maintain
+separate POS accounts for the "parent" Customer as well as the
+Household "shopper".  When a coupon is given it may be enabled for
+both of the accounts, but then when it is redeemed by either it
+becomes disabled for both.
+
+Now, maybe your POS already has a way to link Household accounts, and
+even a way to handle the dynamic coupon example.  But then that sounds
+like you already have a good enough system and don't need Rattail to
+be the Household "system" at all.  Although it could still be used for
+reporting and similar needs, etc.
+
+So if your current situation is "not ideal" then Rattail is here to
+help in whatever way it can; however it's difficult to describe the
+scenarios it might best be suited for, until more real-world scenarios
+are dealt with.