Configure CMake to install the re2Config "export".

Fixes #201.

Change-Id: I66d948c197c3c8875a72a9547efb14790b5e7bb1
Reviewed-on: https://code-review.googlesource.com/c/re2/+/40030
Reviewed-by: Paul Wankadia <junyer@google.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index f87c4ff..f29562c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -147,4 +147,5 @@
     )
 
 install(FILES ${RE2_HEADERS} DESTINATION include/re2)
-install(TARGETS re2 ARCHIVE DESTINATION lib LIBRARY DESTINATION lib RUNTIME DESTINATION bin)
+install(TARGETS re2 EXPORT re2Config ARCHIVE DESTINATION lib LIBRARY DESTINATION lib RUNTIME DESTINATION bin INCLUDES DESTINATION include)
+install(EXPORT re2Config DESTINATION lib/cmake/re2)