Update Test-Running Command in Documentation (#575)

This pull request updates the test-running command in the documentation
to reflect the correct path for the test executable. The command should
be:

./build/tests/runner --gtest_brief=1

This change ensures that users follow the correct procedure for running
tests after building the project.

icicle/README.md

@@ -6,7 +6,7 @@
 mkdir -p build;
 cmake -DBUILD_TESTS=ON -DCURVE=<supported_curve> -S . -B build;
 cmake --build build;
-./build/runner --gtest_brief=1
+./build/tests/runner --gtest_brief=1
 ```
 
 The command above will build ICICLE Core and run the ctest.