Reword documentation

Test: N/A, documentation change only.

Bug: 267208956
Change-Id: Iadc04f771560ed080a0f93338aef8459c9ddb3c8

README.md

@@ -105,31 +105,35 @@ Android.bp files can contain C-style multiline `/* */` and C++ style single-line
 
 ### Types
 
-Variables and properties are strongly typed, variables dynamically based on the
-first assignment, and properties statically by the module type.  The supported
-types are:
+Variables and properties are strongly typed. Variables are dynamically typed
+based on the first assignment, and properties are statically typed by the
+module type.  The supported types are:
 * Bool (`true` or `false`)
 * Integers (`int`)
 * Strings (`"string"`)
 * Lists of strings (`["string1", "string2"]`)
 * Maps (`{key1: "value1", key2: ["value2"]}`)
 
-Maps may values of any type, including nested maps.  Lists and maps may have
-trailing commas after the last value.
+Maps may contain values of any type, including nested maps. Lists and maps may
+have trailing commas after the last value.
 
 Strings can contain double quotes using `\"`, for example `"cat \"a b\""`.
 
 ### Operators
 
-Strings, lists of strings, and maps can be appended using the `+` operator.
-Integers can be summed up using the `+` operator. Appending a map produces the
-union of keys in both maps, appending the values of any keys that are present
-in both maps.
+The `+` operator:
+* Sums integers.
+* Concatenates strings and lists.
+* Produces the union of maps.
+
+Concatenating maps produces a map whose keys are the union of the given maps'
+keys, and whose mapped values are the union of the given maps' corresponding
+mapped values.
 
 ### Defaults modules
 
-A defaults module can be used to repeat the same properties in multiple modules.
-For example:
+A `defaults` module can be used to repeat the same properties in multiple
+modules. For example:
 
 ```
 cc_defaults {