Document the build-time requirement for nghttp2

PLATFORMS.md

@@ -13,7 +13,7 @@
 In general, this version of BIND will build and run on any POSIX-compliant
 system with a C11-compliant C compiler, BSD-style sockets with RFC-compliant
 IPv6 support, POSIX-compliant threads, the `libuv` asynchronous I/O library,
-and the OpenSSL cryptography library.
+the OpenSSL cryptography library, and the `nghttp2` HTTP/2 library.
 
 The following C11 features are used in BIND 9:
 

README.md

@@ -128,13 +128,13 @@ including your patch as an attachment, preferably generated by
 
 At a minimum, BIND requires a Unix or Linux system with an ANSI C compiler,
 basic POSIX support, and a 64-bit integer type. BIND also requires the
-`libuv` asynchronous I/O library, and a cryptography provider library
-such as OpenSSL or a hardware service module supporting PKCS#11. On
-Linux, BIND requires the `libcap` library to set process privileges,
-though this requirement can be overridden by disabling capability
-support at compile time. See [Compile-time options](#opts) below
-for details on other libraries that may be required to support
-optional features.
+`libuv` asynchronous I/O library, the `nghttp2` HTTP/2 library, and a
+cryptography provider library such as OpenSSL or a hardware service
+module supporting PKCS#11. On Linux, BIND requires the `libcap` library
+to set process privileges, though this requirement can be overridden by
+disabling capability support at compile time. See [Compile-time
+options](#opts) below for details on other libraries that may be
+required to support optional features.
 
 Successful builds have been observed on many versions of Linux and
 Unix, including RHEL/CentOS, Fedora, Debian, Ubuntu, SLES, openSUSE,

doc/notes/notes-current.rst

@@ -52,9 +52,11 @@ New Features
   an optional ``tls`` option which specifies either a previously configured
   ``tls`` statement or ``ephemeral``. [GL #2392]
 
-- ``named`` now supports DNS-over-HTTPS (DoH). Both TLS-encrypted and
-  unencrypted HTTP/2 connections are supported (the latter may be used to
-  offload encryption to other software).
+- Support for DNS-over-HTTPS (DoH) was added to ``named``. Because of
+  this, the ``nghttp2`` HTTP/2 library is now required for building the
+  development branch of BIND 9. Both TLS-encrypted and unencrypted
+  HTTP/2 connections are supported (the latter may be used to offload
+  encryption to other software).
 
   Note that there is no client-side support for HTTPS as yet; this will be
   added to ``dig`` in a future release. [GL #1144]