fix(cmake docs): make output directory before extracting
@@ -100,9 +100,11 @@ Set the following three environment variables:
```shell
$ export KYTHE_ROOT_DIRECTORY="/absolute/path/to/repo/root"
-$ export KYTHE_OUTPUT_DIRECTORY="/tmp/kythe-output"
$ export KYTHE_CORPUS="github.com/myproject/myrepo"
+$ export KYTHE_OUTPUT_DIRECTORY="/tmp/kythe-output"
+$ mkdir -p "$KYTHE_OUTPUT_DIRECTORY"
+
# $CMAKE_ROOT_DIRECTORY is passed into the -sourcedir flag. This value should be
# the directory that contains the top-level CMakeLists.txt file. In many
# repositories this path is the same as $KYTHE_ROOT_DIRECTORY.
