Linters: Add github action, update README

Github action will:

1. Lint
2. Format (err if any diff)
3. Run 'go mod tidy' (err if any diff)

.github/workflows/lint-golang.yml

@@ -0,0 +1,40 @@
+name: Lint golang
+
+on: [push, pull_request]
+
+jobs:
+  go:
+    name: Lint go files
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+
+      - name: Setup go
+        uses: actions/setup-go@v3
+        with:
+          go-version: stable
+
+      - name: Run golangci-lint
+        uses: golangci/golangci-lint-action@v3
+        with:
+          version: latest
+          args: --timeout 5m
+
+      - name: Install gofumpt
+        env:
+          GOFUMPT_VER: 0.5.0
+        run: |
+          mkdir -v -p "$HOME/.local/bin"
+          wget -O "$HOME/.local/bin/gofumpt" "https://github.com/mvdan/gofumpt/releases/download/v${GOFUMPT_VER}/gofumpt_v${GOFUMPT_VER}_linux_amd64"
+          chmod 0700 "$HOME/.local/bin/gofumpt"
+
+      - name: Run gofumpt
+        run: |
+          find . -type f -name '*.go' ! -name '*.pb.go' | xargs -n1 "$HOME/.local/bin/gofumpt" -w -lang=1.21
+          git diff --exit-code
+
+      - name: go mod tidy
+        run: |
+          go mod tidy
+          git diff --exit-code -- go.mod go.sum

README.md

@@ -24,3 +24,22 @@ Schema: ThingSchema(),
 }
 ```
 
+### Running Linters and Formatter
+
+#### Prerequisites
+- [golangci-lint](https://github.com/golangci/golangci-lint)
+- [gofumpt](https://github.com/mvdan/gofumpt)
+
+#### Run the commands
+
+**Linter:**
+```
+$ golangci-lint run --config .golangci.yml 
+```
+
+**Formatter:**
+```
+$ gofumpt -w ./
+
+# -w writes the result to source file.
+```