Add first docs for Rattail DB, and POS / other data stores

docs/data/other.rst

@@ -2,4 +2,33 @@
 POS and Other Data Stores
 =========================
 
-TODO
+Rattail is able to read from and/or write to various other data stores, for
+example:
+
+* POS systems
+* any SQL DB
+* any web API
+* Excel, CSV etc.
+
+When we say that "Rattail is able" to do this, really we mean that all the
+building blocks are there already and implementing specific import/export logic
+should require minimal effort.  In some cases a "common" e.g. POS system may be
+well-supported out of the box.
+
+Supported POS Systems
+---------------------
+
+The following POS systems are considered well-supported.  Integration packages
+for each are continually being developed.  However the nature of integrations
+possible with each of these will vary:
+
+* CORE-POS
+* ECRS Catapult
+* LOC SMS
+
+These systems are not well-supported but have received some amount of attention
+in the past, so are not entirely unknown:
+
+* CAM32
+* Revel
+* ScanMaster