docs: add images & fix typo

docs/index.md

@@ -7,4 +7,6 @@ Flexible test runner for testing Nix code, written in Go.
 - Snapshot, Unit (equal checks) and Script-Tests (unit tests with assertions you could say)
 - Supports testing against raw Nix code or derivation output
 - Simple and easy to read summary of test results
+    ![screenshot](./images/summary_screenshot.png)
 - Junit report support (eg. for displaying the results in GitLab etc.)
+    ![screenshot](./images/gitlab_junit_screenshot.png)

docs/usage.md

@@ -93,7 +93,7 @@ Examples:
     name = "pretty-test";
     # by default it uses json to serialize and compare the values. Derivations
     # and functions don't really work that way though, so you can also use
-    # "pretty" to use lib.generators.pretty
+    # "pretty" to use lib.generators.toPretty
     format = "pretty";
     # you can also set the pos here
     pos = __curPos;