doc: dev-tools: kselftest.rst: update contributing new tests

Add a description that kernel config options should be added into a
config file that is placed next to the newly added test.

Signed-off-by: Anders Roxell <[email protected]>
Reviewed-by: Shuah Khan (Samsung OSG) <[email protected]>
Signed-off-by: Jonathan Corbet <[email protected]>
1 file changed