Update the README.md file

Author: thewizardplusplus

README.md

@@ -5,6 +5,35 @@
 [![Build Status](https://travis-ci.org/thewizardplusplus/go-code-runner.svg?branch=master)](https://travis-ci.org/thewizardplusplus/go-code-runner)
 [![codecov](https://codecov.io/gh/thewizardplusplus/go-code-runner/branch/master/graph/badge.svg)](https://codecov.io/gh/thewizardplusplus/go-code-runner)
 
+The library that implements the compiling and running of a code written in the Go programming language and running of a test case set for the compiled code (i.e. the executable file).
+
+## Features
+
+- saving of a code to a temporary file:
+  - storing of the temporary file with the code to an individual temporary directory;
+- checking of package imports used in the code written in the Go programming language:
+  - checking based on the set of allowed imports;
+- compiling of a code written in the Go programming language:
+  - automatic importing of the packages used in the code (optionally);
+  - checking of package imports used in the code (optionally):
+    - checking based on the set of allowed imports;
+  - enriching of an error of the external command running by an output from the stderr stream;
+  - support for the running time management (via the Go context);
+- running of the compiled code (i.e. the executable file):
+  - passing of a custom input as the stdin stream;
+  - returning of an output from the stdout stream;
+  - enriching of an error of the external command running by an output from the stderr stream;
+  - support for the running time management (via the Go context);
+- running of a test case set for the compiled code (i.e. the executable file):
+  - representation of a test case:
+    - input;
+    - expected output;
+  - checking of an actual output in each test case:
+    - returning of the [sentinel errors](https://dave.cheney.net/2016/04/27/dont-just-check-errors-handle-them-gracefully#sentinel%20errors):
+      - failed running — it returns on a running error;
+      - unexpected output — it returns when the expected and actual outputs do not match;
+  - support for the running time management (via the Go context).
+
 ## Installation
 
 Prepare the directory: