Add new installation instructions & add MacOS workflow

.github/workflows/macos_test.yml

@@ -0,0 +1,16 @@
+name: MacOS latest
+
+on: [push, pull_request]
+
+jobs:
+  on_build_actions:
+    runs-on: macos-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Install package
+        run: |
+          python3 -m pip install --upgrade pip
+          python3 -m pip install pygame
+          python3 -m pip install .
+      - name: Run Tests    
+        run: python3 -m unittest

README.md

@@ -20,8 +20,10 @@ subject to change when this project migrates to the
 becomes a third-party library.
 
 ## Installation
-Please follow [this guide](https://github.com/novialriptide/pygame_geometry/blob/main/BUILD.md)
-to install pygame_geometry.
+### Download an experimental build
+```
+pip install git+https://github.com/novialriptide/pygame_geometry
+```
 
 ## Help
 The documentation is a work in progress, but you can check