Update README to address issue where multiple runtime libraries get linked

Author: sophimao

README.md

@@ -188,8 +188,10 @@ IntelⓇ FPGA RTE for OpenCL™ installed on your system:
 1.  In the IntelⓇ FPGA SDK for OpenCL™ installation directory, source
     the initialization script (see [Running Unit Tests](#running-unit-tests)).
 
-2.  Update the `/etc/OpenCL/vendors/Altera.icd` file with the full path
-    to the `libalteracl.so` library in the runtime installation directory.
+2.  Update the `/etc/OpenCL/vendors/Altera.icd` file with either the partial
+    name `libalteracl.so` if LD_LIBRARY_PATH contains the full path to the 
+    `libalteracl.so` library in the runtime installation directory, or the full
+    path itself.
 
 3.  Compile your OpenCL host program with the OpenCL header files included from
     the runtime installation directory.
@@ -215,8 +217,10 @@ or IntelⓇ FPGA RTE for OpenCL™ installed on your system:
 1.  Download, build, and install the
     [OpenCL ICD Loader](https://github.com/KhronosGroup/OpenCL-ICD-Loader).
 
-2.  Create the `/etc/OpenCL/vendors/Altera.icd` file with the full path
-    to the `libalteracl.so` library in the runtime installation directory.
+2.  Create the `/etc/OpenCL/vendors/Altera.icd` file with either the partial
+    name `libalteracl.so` if LD_LIBRARY_PATH contains the full path to the 
+    `libalteracl.so` library in the runtime installation directory, or the full
+    path itself.
 
 3.  Compile your OpenCL host program with the OpenCL header files included from
     the runtime installation directory.
@@ -233,3 +237,10 @@ or IntelⓇ FPGA RTE for OpenCL™ installed on your system:
     ```
 
 6.  Run your OpenCL host program.
+
+### Notes
+
+-   Check the environment variable OCL_ICD_FILENAMES to make sure it doesn't resolve
+    to any `libalteracl.so` runtime other than the one specified in the 
+    `/etc/OpenCL/vendors/Altera.icd` file. Mismatch will lead to multiple runtime 
+    library instances being linked to the program, causing undefined behaviours.