doc: GTEST_ROOT env variable
@@ -502,6 +502,9 @@ This value specifies the root directory of a local copy of the [Google Test][] f
top level directory of `GTEST_ROOT`. If this file exists, then the build system
will use the sources files at `GTEST_ROOT` to translate tests that use [Google Test][].
+It can be provided as CMake or environment variable.
+If both options are provided the value passed via CMake takes precedence.
+
[Google Test]: https://github.com/google/googletest
It is recommended that you browse through all of the options using `ccmake`.
