Fix mongoose docs generation

PUBLISHED_FROM=331821dcd1f7dc8a94581cd8a9b51aa00a89fddc

docs/c-api/mbuf.h/intro.md

@@ -0,0 +1,20 @@
+---
+title: "Memory Buffers"
+symbol_kind: "intro"
+decl_name: "mbuf.h"
+items:
+  - { name: mbuf_append.md }
+  - { name: mbuf_free.md }
+  - { name: mbuf_init.md }
+  - { name: mbuf_insert.md }
+  - { name: mbuf_remove.md }
+  - { name: mbuf_resize.md }
+  - { name: mbuf_trim.md }
+  - { name: struct_mbuf.md }
+---
+
+Mbufs are mutable/growing memory buffers, like C++ strings.
+Mbuf can append data to the end of a buffer or insert data into arbitrary
+position in the middle of a buffer. The buffer grows automatically when
+needed.
+