Fix mongoose docs generation

PUBLISHED_FROM=331821dcd1f7dc8a94581cd8a9b51aa00a89fddc

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

@@ -0,0 +1,12 @@
+---
+title: "mbuf_append()"
+decl_name: "mbuf_append"
+symbol_kind: "func"
+signature: |
+  size_t mbuf_append(struct mbuf *, const void *data, size_t data_size);
+---
+
+Appends data to the Mbuf.
+
+Returns the number of bytes appended or 0 if out of memory. 
+