Update CONTRIBUTING.md

CONTRIBUTING.md

@@ -8,22 +8,22 @@ Once done (and new tests are written to ensure, a bug is really fixed, and the f
 
 A test usually defines a grammar, optionally some attributes and a Test class.
 It then normally runs RelAST followed by JastAdd.
-To create a new test, the following four ingredients are needed:
+To create a new test, the following four ingredients are involved:
 
 ## Specification
 
 Here, the grammar and attributes to be compiled are contained.
 Use `src/test/jastadd/$YourTestName` as directory to put your files into.
-All generated `*.ast`, `*.jrag` and `ResolverStubs.jrag` are already ignored by the main `.gitignore`.
+All generated `*.ast`, `*.jadd` and `ResolverStubs.jrag` are already ignored by the main `.gitignore`.
 
-## Generated files
+## Generated Java files
 
 Usually, all files are generated into a separate directory in `src/test/java-gen/`.
 This location can be [configured](#build-configuration).
 
 ## Build configuration
 
-Currently, test setup is configured within the `build.gradle` using a specialized Gradle task `RelastTest`.
+Currently, the test setup is configured within `build.gradle` using a specialized Gradle task `RelastTest`.
 An example configuration might look like:
 
 ```groovy
@@ -71,7 +71,7 @@ Furthermore, empty lines, lines starting with `//` and the order of the error me
 ## Output diff
 
 Currently, there is one test to test whether the output of RelAST is a valid input for RelAST and produces the same output again.
-To achieve this, there two Gradle tasks. The first produces the usual `.ast` and `.jadd` files, whereas the second task takes the `.ast` as input.
+To achieve this, there are two Gradle tasks. The first produces the usual `.ast` and `.jadd` files, whereas the second task takes the `.ast` as input.
 The test then ensures, that both output grammars are identical.
 
 # Publishing