spelling fixes + gitignore updates (#67)

similar to fortio/fortio#939

ran https://github.com/codespell-project/codespell (with -w after
review/manual checks/tweaks)

.gitignore

@@ -1,3 +1,5 @@
+*.bak
+.DS_Store
 slack-proxy
 .goreleaser.yaml
 .golangci.yml

README.md

@@ -4,7 +4,7 @@ This tool serves as a proxy for applications aiming to dispatch messages to Slac
 
 ## Use-case
 
-For those managing multiple applications, a practical approach is to create a separate Slack app or webhook for each application. That method is prefered. **However**, if you are operating a singular system, like Alertmanager or Grafana, and wish to avoid the complexities of providing individual teams with:
+For those managing multiple applications, a practical approach is to create a separate Slack app or webhook for each application. That method is preferred. **However**, if you are operating a singular system, like Alertmanager or Grafana, and wish to avoid the complexities of providing individual teams with:
 
 - Their distinct webhooks
 - Unique notification channel keys

server.go

@@ -115,7 +115,7 @@ func (app *App) handleRequest(w http.ResponseWriter, r *http.Request) {
 	// This is the downside of having a queue which could potentially delay responses by a lot.
 	// We do our due diligences on the received message and can make a fair assumption we will be able
 	// to process it.
-	// Application should utlise this applications metrics and logs to find out if there are any issues.
+	// Application should utilize this application's metrics and logs to find out if there are any issues.
 	err := jrpc.Reply[SlackResponse](w, http.StatusOK, &SlackResponse{
 		Ok: true,
 	})