[kotlin] Add ReadMe.md to 'all-tests-compose'

GitOrigin-RevId: f3c7c19447c73100de825b08840dae5e8f5e6671

plugins/kotlin/all-tests-compose/ReadMe.md

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+# Tests with K2 and Compose
+
+## How to create new tests with Compose
+
+To create tests together with Compose, it is required to create a new module for the tests.
+A new module is required because the tests will have to run with the Compose IDE plugin being present at runtime,
+which is not expected for regular tests.
+
+After the module was created, add the module as runtime dependency to this `all-tests-compose` module
+
+- The test packages shall be prefixed with `org.jetbrains.kotlin.idea.compose.k2.*`.
+- The tests will run in aggregate (master & kt-master)
+
+## How to setup the compose compiler
+
+You can use the `tests-compose` utilities module to get access to the `composeCompilerJars`.
+If the compiler is setup (e.g. for debugger evaluate expression), the passing those jars with `-Xplugin` is required.
+
+## How to setup the compose runtime
+
+If the compose runtime is required, then the current maven coordinates can also be found in the`tests-compose` module.