Update readme for macOS (#21952)

README.md

@@ -141,9 +141,6 @@ Prerequisites for Linux:
 
 Prerequisites for macOS:
 - [Apple Developer Tools][getting-started:macos-dev-tools]
-- On macOS 10.14 or below, you will also need:
-  - [Homebrew][getting-started:macos-brew]
-  - [g++][getting-started:macos-gcc] >= 6 from Homebrew
 
 First, download and bootstrap vcpkg itself; it can be installed anywhere,
 but generally we recommend using vcpkg as a submodule for CMake projects.
@@ -205,7 +202,7 @@ If you want to add instructions for your specific distro,
 
 ## Installing macOS Developer Tools
 
-On macOS 10.15, the only thing you should need to do is run the following in your terminal:
+On macOS, the only thing you should need to do is run the following in your terminal:
 
 ```sh
 $ xcode-select --install
@@ -213,25 +210,6 @@ $ xcode-select --install
 
 Then follow along with the prompts in the windows that comes up.
 
-On macOS 10.14 and previous, you'll also need to install g++ from homebrew;
-follow the instructions in the following section.
-
-### Installing GCC for macOS before 10.15
-
-This will _only_ be necessary if you're using a macOS version from before 10.15.
-Installing homebrew should be very easy; check out <brew.sh> for more information,
-but at its simplest, run the following command:
-
-```sh
-$ /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install.sh)"
-```
-
-Then, in order to grab an up-to-date version of gcc, run the following:
-
-```sh
-$ brew install gcc
-```
-
 You'll then be able to bootstrap vcpkg along with the [quick start guide](#quick-start-unix)
 
 ## Using vcpkg with CMake
@@ -312,7 +290,7 @@ To enable tab-completion in the shell of your choice, run:
 or
 
 ```sh
-$ ./vcpkg integrate bash
+$ ./vcpkg integrate bash # or zsh
 ```
 
 depending on the shell you use, then restart your console.