Update CONTRIBUTION.md for path to slang-test.exe (shader-slang#4619)

The path to slang-test.exe has been changed recently and it needs to be updated on the document.

Author: jkwak-work

CONTRIBUTION.md

@@ -111,6 +111,8 @@ Make your changes and ensure to follow our [Design Decisions](docs/design/README
 ### Testing
 Test your changes thoroughly to ensure they do not introduce new issues. This is done by building and running a "slang-test" from the repository root directory. For more details about "slang-test", please refer to a [Documentation on testing](tools/slang-test/README.md).
 
+> Note: slang-test is meant to launch from the root of the repository. It uses a hard-coded directory name "tests/" that is expected to exist in the current working directory.
+
 > Note: One of the options for `slang-test.exe` is `-api`, and it takes an additional keyword to specify which API to test. When the option is `-api all-cpu`, as an example, it means it tests all APIs except CPU. The minus sign (-) after `all` means "exclude" and you can "include" with plus sign (+) like `-api gl+dx11`.
 
 If you are familiar with Workflow/Actions in github, you can check [Our Workflows](.github/workflows). "Test Slang" section in [ci.yml](.github/workflows/ci.yml) is where "slang-test" runs.
@@ -125,7 +127,7 @@ For a quick reference, follow the instructions below.
    ```
 1. Run slang-test with multiple threads. This may take 10 minutes or less depending on the performance of your computer.
    ```
-   C:\git\slang> bin\windows-x64\release\slang-test.exe -use-test-server -server-count 8
+   C:\git\slang> build\Release\bin\slang-test.exe -use-test-server -server-count 8
    ```
    > Note: if you increase `-server-count` more than 16, you may find some of tests randomly fail. This is a known issue on the graphics driver side.
 1. Check whether the test is finished as expected.
@@ -138,7 +140,7 @@ For a quick reference, follow the instructions below.
    ```
 1. Run slang-test with multiple threads. This may take 10 minutes or less depending on the performance of your computer.
    ```
-   $ ./bin/linux-x64/release/slang-test  -use-test-server -server-count 8
+   $ ./build/Release/bin/slang-test -use-test-server -server-count 8
    ```
 1. Check whether the test is finished as expected.