Added instruction for existing ZLIB configuration
Using two configuration flags `DZLIB_INCLUDE_DIR` and `DZLIB_LIB` we can locate an existing ZLIB on the system
diff --git a/cmake/README.md b/cmake/README.md
index 1e7410d..305ebb8 100644
--- a/cmake/README.md
+++ b/cmake/README.md
@@ -302,6 +302,11 @@
If it reports NOTFOUND for zlib_include or zlib_lib, you might haven't put
the headers or the .lib file in the right directory.
+If you already have ZLIB library and headers at some other location on your system then alternatively you can define following configuration flags to locate them:
+
+ -DZLIB_INCLUDE_DIR=<path to dir containing zlib headers>
+ -DZLIB_LIB=<path to dir containing zlib>
+
Build and testing protobuf as usual.
Notes on Compiler Warnings
