THRIFT-3148 Markdown links to coding_standards are dead

This closes #491
diff --git a/lib/cpp/coding_standards.md b/lib/cpp/coding_standards.md
index fac5056..8018c77 100644
--- a/lib/cpp/coding_standards.md
+++ b/lib/cpp/coding_standards.md
@@ -1,4 +1,4 @@
-Please follow [General Coding Standards](/coding_standards)
+Please follow [General Coding Standards](/doc/coding_standards.md)
 
  * see .clang-format in root dir for settings of accepted format
  * clang-format (3.5 or newer) can be used to automaticaly reformat code ('make style' command)