Created FloatAttribute precision (markdown)

FloatAttribute-precision.md

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+The `Precision` field in the `FloatAttribute` struct controls how many decimal places are used to represent the value when it's converted to a `string`. This affects the value of `GetStringFromSysVal`, and hence the value of `GetClass`, `DecomposeOnAttributeValues` and every other function which depends on a string class variable. 
+
+By default, `Precision` is set to two.
+
+**Code excerpt: Setting the precision of all FloatAttributes on a set of instances to one decimal place.**
+```go
+for _, a := range pred.AllAttributes() {
+    af, ok := a.(*base.FloatAttribute)
+    if !ok {
+       panic("All of these should be FloatAttributes!")
+    }
+    af.Precision = 1
+}
+```
+