Fix Homebrew paths in MacOS install instructions (#160)

Homebrew switched install locations a while back when Apple started shipping their own ARM processors on desktop, which broke the old install instructions.

This updates the instructions to account for it.

Author: Mr0grog

README.md

@@ -45,9 +45,17 @@ This package was originally built as a component of EDGI’s [Web Monitoring Pro
 
     The `--no-binary` flag ensures that pip downloads and builds a fresh copy of `lxml` (one of web-monitoring-diff’s dependencies) rather than using a pre-built version. It’s slower to install, but is required for all the dependencies to work correctly together. **If you publish a package that depends on web-monitoring-diff, your package will need to be installed with this flag, too.**
 
-    **On MacOS,** you may need additional configuration to get `pycurl` to use the Homebrew `openssl`. Try the following:
+    **On MacOS,** you may need additional configuration to get `pycurl` to use the Homebrew `openssl`. Try one of the following:
 
     ```sh
+    # Homebrew install locations vary by architechture.
+    # For Apple silicon/ARM:
+    PYCURL_SSL_LIBRARY=openssl \
+      LDFLAGS="-L/opt/homebrew/opt/openssl/lib" \
+      CPPFLAGS="-I/opt/homebrew/opt/openssl/include" \
+      pip install web-monitoring-diff --no-binary lxml --no-cache-dir
+
+    # Or for Intel:
     PYCURL_SSL_LIBRARY=openssl \
       LDFLAGS="-L/usr/local/opt/openssl/lib" \
       CPPFLAGS="-I/usr/local/opt/openssl/include" \