added a troubleshooting section for macOS mojave

installation/on_mac_osx_using_homebrew.md

@@ -21,3 +21,21 @@ you need to reinstall the command line tools and then select the default active
 $ xcode-select --install
 $ xcode-select --switch /Library/Developer/CommandLineTools
 ```
+
+## Troubleshooting on macOS MacOS 10.14.2 (Mojave)
+
+if you get an error like:
+
+```
+ld: library not found for -lssl (this usually means you need to install the development package for libssl)
+```
+
+you may need to install OpenSSL and link pkg-config to OpenSSL
+
+```
+brew install openssl
+```
+
+```
+export PKG_CONFIG_PATH=$PKG_CONFIG_PATH:/usr/local/opt/openssl/lib/pkgconfig
+```