README: Add explicit UNIX reference into the relevant installation sections (#2744)

Co-authored-by: Ivan Pozdeev <vano@mail.mipt.ru>

README.md

@@ -44,10 +44,11 @@ This project was forked from [rbenv](https://github.com/rbenv/rbenv) and
   * [Locating Pyenv-provided Python Installations](#locating-pyenv-provided-python-installations)
 * **[Installation](#installation)**
   * [Getting Pyenv](#getting-pyenv)
-    * [Homebrew in macOS](#homebrew-in-macos)
+    * [UNIX/MacOS](#unixmacos)
+      * [Homebrew in macOS](#homebrew-in-macos)
+      * [Automatic installer](#automatic-installer)
+      * [Basic GitHub Checkout](#basic-github-checkout)
     * [Windows](#windows)
-    * [Automatic installer](#automatic-installer)
-    * [Basic GitHub Checkout](#basic-github-checkout)
   * [Set up your shell environment for Pyenv](#set-up-your-shell-environment-for-pyenv)
   * [Restart your shell](#restart-your-shell)
   * [Install Python build dependencies](#install-python-build-dependencies)
@@ -200,7 +201,8 @@ As far as Pyenv is concerned, version names are simply directories under
 ## Installation
 
 ### Getting Pyenv
-#### Homebrew in macOS
+#### UNIX/MacOS
+##### Homebrew in macOS
 
    1. Consider installing with [Homebrew](https://brew.sh):
       ```sh
@@ -234,19 +236,7 @@ As far as Pyenv is concerned, version names are simply directories under
         ~~~
 
 
-#### Windows
-
-Pyenv does not officially support Windows and does not work in Windows outside
-the Windows Subsystem for Linux.
-Moreover, even there, the Pythons it installs are not native Windows versions
-but rather Linux versions running in a virtual machine --
-so you won't get Windows-specific functionality.
-
-If you're in Windows, we recommend using @kirankotari's [`pyenv-win`](https://github.com/pyenv-win/pyenv-win) fork --
-which does install native Windows Python versions.
-
-
-#### Automatic installer
+##### Automatic installer
 
 `curl https://pyenv.run | bash`
 
@@ -254,7 +244,7 @@ For more details visit our other project:
 https://github.com/pyenv/pyenv-installer
 
 
-#### Basic GitHub Checkout
+##### Basic GitHub Checkout
 
 This will get you going with the latest version of Pyenv and make it
 easy to fork and contribute any changes back upstream.
@@ -270,6 +260,18 @@ easy to fork and contribute any changes back upstream.
     cd ~/.pyenv && src/configure && make -C src
     ```
 
+#### Windows
+
+Pyenv does not officially support Windows and does not work in Windows outside
+the Windows Subsystem for Linux.
+Moreover, even there, the Pythons it installs are not native Windows versions
+but rather Linux versions running in a virtual machine --
+so you won't get Windows-specific functionality.
+
+If you're in Windows, we recommend using @kirankotari's [`pyenv-win`](https://github.com/pyenv-win/pyenv-win) fork --
+which does install native Windows Python versions.
+
+
 ### Set up your shell environment for Pyenv
 
 **Upgrade note:** The startup logic and instructions have been updated for simplicity in 2.3.0.