Add notes about the environment variables and install location customization

Author: cmcgee1024

install/linux/swiftly/index.md

@@ -29,6 +29,8 @@ Run the following command in your terminal, to configure swiftly for your accoun
 SWIFTLY_HOME_DIR=~/.swiftly SWIFTLY_BIN_DIR=~/.swiftly/bin ./swiftly init
 ```
 
+Note: You can adjust the SWIFTLY_* environment variables to customize the install location, or remove them entirely to a Linux standard location.
+
 Your current shell may need some additional steps to update your session. Follow the guidance at the end of the installation for a smooth install experience, such as sourcing the environment file, and rehashing your shell's PATH.
 
 There can be certain packages that need to be installed on your system so that the Swift toolchain can function. The swiftly initialization routine will show you how to install any missing packages.

install/macos/swiftly/index.md

@@ -17,6 +17,8 @@ Run the following command in your terminal, to configure swiftly for your accoun
 SWIFTLY_HOME_DIR=~/.swiftly SWIFTLY_BIN_DIR=~/.swiftly/bin ~/.swiftly/bin/swiftly init
 ```
 
+Note: You can change the SWIFTLY_* environment variables to customize the install location, or remove them to use a macOS standard location.
+
 <div class="warning" markdown="1">
 Your current shell may need some additional steps to update your session. Follow the guidance at the end of the installation for a smooth install experience, such as sourcing the environment file, and rehashing your shell's PATH.
 </div>