Add zstd as a build dependency and add note for Python 3.14 and compression.zstd.

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@@ -12,13 +12,20 @@ compilation succeeds but the new Python version exhibits weird failures at
 runtime. The following instructions are our recommendations for a sane build
 environment.
 
+_**Note**_
+
+Python 3.14 adds support for a `compression.zstd` module that depends on zstd
+version 1.4.5 or newer. This version is not available in some extended-release
+distros like Alma/Rocky Linux 8 and Ubuntu 20.04. See [PEP 
+784](https://peps.python.org/pep-0784/) for more details.
+
 * **Mac OS X:**
 
     If you haven't done so, install Xcode Command Line Tools
     (`xcode-select --install`) and [Homebrew](http://brew.sh/). Then:
 
     ```sh
-    brew install openssl readline sqlite3 xz zlib tcl-tk@8 libb2
+    brew install openssl readline sqlite3 xz zlib tcl-tk@8 libb2 zstd
     ```
     
     For older operating systems `Homebrew` might not be available so install `pyenv` with: 
@@ -40,7 +47,7 @@ environment.
     For dependencies use [MacPorts](https://www.macports.org/install.php):
 
     ```sh
-    sudo port install pkgconfig openssl zlib xz gdbm tcl tk +quartz sqlite3 sqlite3-tcl
+    sudo port install pkgconfig openssl zlib xz gdbm tcl tk +quartz sqlite3 sqlite3-tcl zstd
     ```
 
 * **Ubuntu/Debian/Mint:**
@@ -51,6 +58,8 @@ environment.
     libncursesw5-dev xz-utils tk-dev libxml2-dev libxmlsec1-dev libffi-dev liblzma-dev
     ```
 
+    Additionally, you should install `libstd-dev` if you are building Python 3.14 or newer but note that Ubuntu 20.04 does not include a sufficiently new version of this package to build the `compression.zstd` module.
+
     The Python's documentation reports a different set of dependencies in the [documentation](https://devguide.python.org/getting-started/setup-building/#build-dependencies) and in the script used in the [GitHub Actions](https://github.com/python/cpython/blob/main/.github/workflows/posix-deps-apt.sh) 
 
     If you are going build PyPy from source or install other Python flavors that require CLang, also install `llvm`.
@@ -61,24 +70,31 @@ environment.
     yum install gcc make patch zlib-devel bzip2 bzip2-devel readline-devel sqlite sqlite-devel openssl-devel tk-devel libffi-devel xz-devel
     ```
 
+    Additionally, you should install `zstd-devel` if you are building Python 3.14 or newer but note that Python requires zstd 1.4.5 or newer, which may not be available in the default package repositories.
+
 * **Amazon Linux 2:**
 
     ```sh
     yum install gcc make patch zlib-devel bzip2 bzip2-devel readline-devel sqlite sqlite-devel openssl11-devel tk-devel libffi-devel xz-devel
     ```
+
+    Additionally, you should install `zstd-devel` if you are building Python 3.14 or newer but note that Python requires zstd 1.4.5 or newer, which may not be available in the default package repositories.
+
 * **Fedora 22 and above:**
 
     ```sh
     dnf install make gcc patch zlib-devel bzip2 bzip2-devel readline-devel sqlite sqlite-devel openssl-devel tk-devel libffi-devel xz-devel libuuid-devel gdbm-libs libnsl2
     ```
 
+    Additionally, you should install `zstd-devel` if you are building Python 3.14 or newer but note that Python requires zstd 1.4.5 or newer, which may not be available in the default package repositories.
+
 *  **Fedora Silverblue**
 
     ```sh
     toolbox enter
     sudo dnf update vte-profile  # https://github.com/containers/toolbox/issues/390
     sudo dnf install "@Development Tools" zlib-devel bzip2 bzip2-devel readline-devel sqlite \
-    sqlite-devel openssl-devel xz xz-devel libffi-devel findutils tk-devel
+    sqlite-devel openssl-devel xz xz-devel libffi-devel findutils tk-devel zstd-devel
     ```
 
 * **openSUSE:**
@@ -88,23 +104,25 @@ environment.
     readline-devel zlib-devel tk-devel libffi-devel sqlite3-devel gdbm-devel make findutils patch
     ```
 
+    Additionally, you should install `libzstd-devel` if you are building Python 3.14 or newer but note that Python requires zstd 1.4.5 or newer, which may not be available in the default package repositories.
+
 * **Arch Linux:**
 
     ```sh
-    pacman -S --needed base-devel openssl zlib xz tk
+    pacman -S --needed base-devel openssl zlib xz tk zstd
     ```
 
 * **Solus:**
 
     ```
     sudo eopkg it -c system.devel
-    sudo eopkg install git gcc make zlib-devel bzip2-devel readline-devel sqlite3-devel openssl-devel tk-devel
+    sudo eopkg install git gcc make zlib-devel bzip2-devel readline-devel sqlite3-devel openssl-devel tk-devel zstd-devel
     ```
 
 * **Alpine Linux:**
 
     ```sh 
-    apk add --no-cache git bash build-base libffi-dev openssl-dev bzip2-dev zlib-dev xz-dev readline-dev sqlite-dev tk-dev
+    apk add --no-cache git bash build-base libffi-dev openssl-dev bzip2-dev zlib-dev xz-dev readline-dev sqlite-dev tk-dev zstd-dev
     ```
 
     * Installation of Python 3.7 may fail due to Python 3.7.0 issue [#34555](https://bugs.python.org/issue34555). A workaround is to install the [linux system headers package](https://pkgs.alpinelinux.org/packages?name=linux-headers&branch=edge):
@@ -116,7 +134,7 @@ environment.
 * **Void Linux:**
 
     ```sh
-    xbps-install base-devel libffi-devel bzip2-devel openssl openssl-devel readline readline-devel sqlite-devel xz liblzma-devel zlib zlib-devel
+    xbps-install base-devel libffi-devel bzip2-devel openssl openssl-devel readline readline-devel sqlite-devel xz liblzma-devel zlib zlib-devel libzstd-devel
     ```