[readme] add reference to brew info for env vars

I encountered a problem during installation where python could not find zlib. It appears there needs to be additional environment variables set, which are provided (and kept up to date) by the brew info command

Author: teaforthecat

README.md

@@ -95,6 +95,7 @@ In **PowerShell** or in a **Command Prompt** window:
     brew install zlib openssl readline
     CFLAGS="-I$(brew --prefix openssl)/include -I$(brew --prefix readline)/include -I$(xcrun --show-sdk-path)/usr/include" LDFLAGS="-L$(brew --prefix openssl)/lib -L$(brew --prefix readline)/lib -L$(brew --prefix zlib)/lib"
     ```
+    Run `brew info` to get the latest environment variable export suggestions, such as `brew info zlib`
 
 - **Windows**
 
@@ -256,4 +257,4 @@ for testing purposes, even though the Elastic Beanstalk team tests the EB CLI ag
 
 ### 5. License
 
-This library is licensed under the Mozilla Public License Version 2.0.
+This library is licensed under the Mozilla Public License Version 2.0.