docs: add yrx_compiler_add_include_dir in C API. (#447)

Add yrx_compiler_add_include_dir from 45a03c6 into the C API documentation.

Author: jtpox

site/content/docs/api/c.md

@@ -230,6 +230,24 @@ This origin is shown in error reports.
 
 ------
 
+#### yrx_compiler_add_include_dir
+
+```c
+enum YRX_RESULT yrx_compiler_add_include_dir(
+    struct YRX_COMPILER *compiler,
+    const char *dir);
+```
+
+Adds a directory to the list of directories where the compiler should look for included files.
+
+When an `include` is found, the compiler looks for the included file in the directories added
+with this function, in the order they were added.
+
+If this function is not called, the compiler will only look for included files in the current
+directory.
+
+------
+
 #### yrx_compiler_ignore_module
 
 ```c

site/hugo_stats.json

@@ -673,6 +673,7 @@
       "yrx_buffer_destroy",
       "yrx_compile",
       "yrx_compiler",
+      "yrx_compiler_add_include_dir",
       "yrx_compiler_add_source",
       "yrx_compiler_add_source_with_origin",
       "yrx_compiler_ban_module",