Update README.md - use relative links to files

compiler/extensions/cpp/README.md

@@ -31,7 +31,7 @@ Although newer C++ compilers are not tested, they should work as well as long as
 
 ## Using Zserio CMake Helper
 
-Zserio provides [`zserio_compiler.cmake`](https://github.com/ndsev/zserio/blob/master/cmake/zserio_compiler_cmake) helper, which defines custom function `zserio_generate_cpp`.
+Zserio provides [`zserio_compiler.cmake`](../../../cmake/zserio_compiler.cmake) helper, which defines custom function `zserio_generate_cpp`.
 This function can be used for automatic generation of C++ sources from zserio schemas.
 
 #### Prerequisites
@@ -162,7 +162,7 @@ The following describes features which minimize the risk of Zserio C++ runtime l
 
 #### Clang-tidy Usage
 
-Clang-tidy tool is run using [this configuration](https://github.com/ndsev/zserio/blob/master/compiler/extensions/cpp/runtime/ClangTidyConfig.txt).
+Clang-tidy tool is run using [this configuration](runtime/ClangTidyConfig.txt).
 The clang-tidy report from the latest C++ runtime library is available [here](https://zserio.org/doc/runtime/latest/cpp/clang-tidy/clang-tidy-report.txt).
 
 Due to compatibility and functional safety considerations, zserio is constrained to utilize the C++11 standard.