Added documentation about clang-uml-wrapped script for Nix

docs/common_options.md

@@ -11,6 +11,7 @@
   * [Use '--query-driver' command line option](#use---query-driver-command-line-option)
   * [Manually add and remove compile flags from the compilation database](#manually-add-and-remove-compile-flags-from-the-compilation-database)
   * [Using 'CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES'](#using-cmake_cxx_implicit_include_directories)
+  * [Nix wrapper](#nix-wrapper)
 
 <!-- tocstop -->
 
@@ -224,4 +225,12 @@ Yet another option, for CMake based projects, is to use the following CMake opti
 set(CMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES ${CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES})
 ```
 
+### Nix wrapper
+On NixOS or when using `nix`, `clang-uml` provides a wrapper script called
+`clang-uml-wrapped`, which builds and exports `CPATH` and `CPLUS_INCLUDE_PATH`
+environment variables before running `clang-uml`, which contain valid
+system header Clang paths for the current Nix environment.
 
+The `clang-uml-wrapped` script can be called the same way as `clang-uml` and
+should resolve the system include paths without the need for any of the above
+solutions.

docs/troubleshooting.md

@@ -11,8 +11,8 @@
   * [Cannot generate diagrams from header-only projects](#cannot-generate-diagrams-from-header-only-projects)
   * [YAML anchors and aliases are not fully supported](#yaml-anchors-and-aliases-are-not-fully-supported)
   * [Schema validation error is thrown, but the configuration file is correct](#schema-validation-error-is-thrown-but-the-configuration-file-is-correct)
-* [Class diagrams](#class-diagrams)
   * ["fatal error: 'stddef.h' file not found"](#fatal-error-stddefh-file-not-found)
+* [Class diagrams](#class-diagrams)
   * [How can I generate class diagram of my entire project](#how-can-i-generate-class-diagram-of-my-entire-project)
   * [Cannot generate classes for 'std' namespace](#cannot-generate-classes-for-std-namespace)
 * [Sequence diagrams](#sequence-diagrams)
@@ -224,8 +224,6 @@ schema validation, and exits if the configuration file is invalid.
 In case there is a bug in the schema validation, the schema validation
 step can be skipped by providing `--no-validate` command line option.
 
-## Class diagrams
-
 ### "fatal error: 'stddef.h' file not found"
 
 This error means that Clang cannot find some standard headers in include
@@ -285,6 +283,8 @@ clang-uml --add-compile-flag -I/opt/my_toolchain/include \
 Also see
 [here](./md_docs_2common__options.html#resolving-include-path-and-compiler-flags-issues).
 
+## Class diagrams
+
 ### How can I generate class diagram of my entire project
 
 I want to generate a diagram containing all classes and relationships in my