docs: add necessary setup for nghttp3

Now nghttp3 has submodules
https://github.com/ngtcp2/nghttp3/blob/main/.gitmodules

Closes #12859

diff --git a/docs/HTTP3.md b/docs/HTTP3.md
index 851a0c46849ff639aad0e13f087bf7c16f4f567f..b09fb94e57fd28b3809ec55b3804710ad6990300 100644 (file)
--- a/docs/HTTP3.md
+++ b/docs/HTTP3.md
@@ -58,6 +58,7 @@ Build nghttp3
      % cd ..
      % git clone -b v1.1.0 https://github.com/ngtcp2/nghttp3
      % cd nghttp3
+     % git submodule update --init
      % autoreconf -fi
      % ./configure --prefix=<somewhere2> --enable-lib-only
      % make