deps: maintaining ngtcp2 and nghttp3

deps/ngtcp2/.gitignore

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+**/*/CMakeLists.txt
+**/*/*.am
+**/*/*.h.in
+**/*/*.pc.in

doc/guides/maintaining-ngtcp2-nghttp3.md

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+# Maintaining ngtcp2 and nghttp3
+
+The ngtcp2 and nghttp3 libraries form the foundation of the QUIC
+implementation. They are acquired from the [ngtcp2/ngtcp2][] and
+[ngtcp2/nghttp3][] repositories on GitHub.
+
+ngtcp2 and nghttp3 are tightly related. They will typically be
+updated together.
+
+## Updating ngtcp2
+
+Update ngtcp2:
+```shell
+git clone https://github.com/ngtcp2/ngtcp2
+cd ngtcp2
+autoreconf -i
+./configure --enable-lib-only
+cd ..
+cp -R ngtcp2/crypto node/deps/ngtcp2
+cp -R ngtcp2/lib node/deps/ngtcp2
+```
+
+The `autoreconf -i` and `./configure --enable-lib-only` commands
+ensure that the necessary template files (such as version.h.in
+located in lib/includes/ngtcp2/ are processed appropriately.
+
+Check that Node.js still builds and tests.
+
+## Updating nghttp3
+
+Update nghttp3:
+```shell
+git clone https://github.com/ngtcp2/nghttp3
+cd nghttp3
+autoreconf -i
+./configure --enable-lib-only
+cd ..
+cp -R nghttp3/lib node/deps/nghttp3
+```
+
+The `autoreconf -i` and `./configure --enable-lib-only` commands
+ensure that the necessary template files (such as version.h.in
+located in lib/includes/ngtcp2/ are processed appropriately.
+
+Check that Node.js still builds and tests.
+
+## Commiting ngtcp2 and nghttp3
+
+Use: `git add --all deps/ngtcp2` and `git add --all deps/nghttp3`
+
+Commit the changes with a message like
+```text
+deps: update ngtcp2 and nghttp3
+
+Updated as described in doc/guides/maintaining-ngtcp2-nghttp3.md.
+```
+
+[ngtcp2/nghttp3]: https://github.com/ngtcp2/nghttp3
+[ngtcp2/ngtcp2]: https://github.com/ngtcp2/ngtcp2