Updates to clarify when to use the -D_GLIBCXX_USE_CXX11_ABI=0 flag

Author: nealwu

tutorials/embedding/README.md

@@ -29,10 +29,9 @@ TF_LFLAGS=( $(python -c 'import tensorflow as tf; print(" ".join(tf.sysconfig.ge
 g++ -std=c++11 -shared word2vec_ops.cc word2vec_kernels.cc -o word2vec_ops.so -fPIC ${TF_CFLAGS[@]} ${TF_LFLAGS[@]} -O2 -D_GLIBCXX_USE_CXX11_ABI=0
 ```
 
-On Mac, add `-undefined dynamic_lookup` to the g++ command.
+On Mac, add `-undefined dynamic_lookup` to the g++ command. The flag `-D_GLIBCXX_USE_CXX11_ABI=0` is included to support newer versions of gcc. However, if you compiled TensorFlow from source using gcc 5 or later, you may need to exclude the flag. Specifically, if you get an error similar to the following: `word2vec_ops.so: undefined symbol: _ZN10tensorflow7strings6StrCatERKNS0_8AlphaNumES3_S3_S3_` then you likely need to exclude the flag.
 
-(The flag `-D_GLIBCXX_USE_CXX11_ABI=0` is included to support newer versions of gcc. However, if you compiled TensorFlow from source using gcc 5 or later, you may need to exclude the flag.)
-Then run using:
+Once you've successfully compiled the ops, run the model as follows:
 
 ```shell
 python word2vec_optimized.py \