Update README.md

Some initial documentation of `dataType` usage.

README.md

@@ -32,6 +32,46 @@ To use it you need `jugglingdb@0.2.x`.
 ## Running tests
 
     npm test
+    
+## Using the `dataType` field/column option with MySQL
+
+The jugglingdb MySQL adapter now supports using the `dataType`  column/property attribute to specify what MySQL column type is used for many jugglingdb types.
+
+The following type-dataType combinations are supported (incomplete):
+* Number
+  * integer types
+     * tinyint
+     * smallint
+     * mediumint
+     * int
+     * bigint
+     * use the 'limit' option to alter the display width
+     * example:
+       `{ count : { type: Number, dataType: 'smallInt' }}`
+  * floating point types
+     * float
+     * double
+     * use the `precision` and `scale` options to specify custom precision. Default is (16,8).
+     * example:
+      `{ average : { type: Number, dataType: 'float', precision: 20, scale: 4 }}`
+  * fixed-point exact value types
+     * decimal
+     * numeric
+     * use the `precision` and `scale` options to specify custom precision. Default is (9,2).
+     * these aren't likely to function as true fixed-point.
+     * example:
+      `{ stdDev : { type: Number, dataType: 'decimal', precision: 12, scale: 8 }}`
+* String / Schema.Text / Schema.JSON
+  * varchar
+  * char
+  * text
+  * mediumtext
+  * tinytext
+  * longtext
+* Date
+  * datetime
+  * timestamp
+    
 
 ## MIT License