CONFIG: Update GitHub Actions trigger (#295)

* CONFIG: Update GitHub Actions trigger

* ENHANCE: Cache GitHub Actions pip

* DOCS: Update README.md to show support for Python >3.9

---------

Co-authored-by: Stefanus Kurniawan <stefanus.kurniawan@deakin.edu.au>
Co-authored-by: Zac Brannelly <zac.brannelly@gmail.com>

.github/workflows/build.yml

@@ -4,6 +4,11 @@ on:
   pull_request:
     branches:
       - "*"
+  push:
+    branches:
+      - main
+    tags:
+      - "v+[0-9]+.[0-9]+.[0-9]*$"
 
 # Cancel in-progress workflow runs on new PR commits.
 concurrency:
@@ -17,9 +22,11 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - name: Set up Python 3.9.5
-        uses: actions/setup-python@v3
+        uses: actions/setup-python@v4
         with:
           python-version: "3.9.5"
+          cache: 'pip'
+          cache-dependency-path: '**/requirements.txt'
       - name: Install tox
         run: |
           # Install tox
@@ -41,9 +48,11 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - name: Set up Python 3.9.5
-        uses: actions/setup-python@v3
+        uses: actions/setup-python@v4
         with:
           python-version: "3.9.5"
+          cache: 'pip'
+          cache-dependency-path: '**/requirements.txt'
       - name: Install tox
         run: |
           # Install tox

surround/README.md

@@ -11,7 +11,7 @@ For more information about Surround library, see [Surround Library](https://surr
 ## Installation
 
 ### Prerequisites
-- [Python](https://www.python.org/) 3+ (Tested on 3.6.5)
+- [Python](https://www.python.org/) 3.9+ (Tested on 3.9.5)
 
 Use package manager [pip](https://pip.pypa.io/en/stable/) to install the latest (stable) version:
 ```