Update README.md, replace master to main (#862)

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## What type of PR is this? (check all applicable)

- [ ] Refactor
- [ ] Feature
- [ ] Bug Fix
- [ ] Optimization
- [x] Documentation Update
- [ ] Go Version Update
- [ ] Dependency Update

## Description

## Related Tickets & Documents

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- Related Issue #
- Closes #

## Added/updated tests?

- [ ] Yes
- [x] No
- [ ] I need help with writing tests

## Run verifications and test

- [ ] `make verify` is passing
- [ ] `make test` is passing

README.md

@@ -13,11 +13,11 @@ Gorilla WebSocket is a [Go](http://golang.org/) implementation of the [WebSocket
 ### Documentation
 
 * [API Reference](https://pkg.go.dev/github.com/gorilla/websocket?tab=doc)
-* [Chat example](https://github.com/gorilla/websocket/tree/master/examples/chat)
-* [Command example](https://github.com/gorilla/websocket/tree/master/examples/command)
-* [Client and server example](https://github.com/gorilla/websocket/tree/master/examples/echo)
-* [File watch example](https://github.com/gorilla/websocket/tree/master/examples/filewatch)
-* [Write buffer pool example](https://github.com/gorilla/websocket/tree/master/examples/bufferpool)
+* [Chat example](https://github.com/gorilla/websocket/tree/main/examples/chat)
+* [Command example](https://github.com/gorilla/websocket/tree/main/examples/command)
+* [Client and server example](https://github.com/gorilla/websocket/tree/main/examples/echo)
+* [File watch example](https://github.com/gorilla/websocket/tree/main/examples/filewatch)
+* [Write buffer pool example](https://github.com/gorilla/websocket/tree/main/examples/bufferpool)
 
 ### Status
 
@@ -33,4 +33,4 @@ package API is stable.
 
 The Gorilla WebSocket package passes the server tests in the [Autobahn Test
 Suite](https://github.com/crossbario/autobahn-testsuite) using the application in the [examples/autobahn
-subdirectory](https://github.com/gorilla/websocket/tree/master/examples/autobahn).
+subdirectory](https://github.com/gorilla/websocket/tree/main/examples/autobahn).

examples/chat/README.md

@@ -38,7 +38,7 @@ sends them to the hub.
 ### Hub 
 
 The code for the `Hub` type is in
-[hub.go](https://github.com/gorilla/websocket/blob/master/examples/chat/hub.go). 
+[hub.go](https://github.com/gorilla/websocket/blob/main/examples/chat/hub.go). 
 The application's `main` function starts the hub's `run` method as a goroutine.
 Clients send requests to the hub using the `register`, `unregister` and
 `broadcast` channels.
@@ -57,7 +57,7 @@ unregisters the client and closes the websocket.
 
 ### Client
 
-The code for the `Client` type is in [client.go](https://github.com/gorilla/websocket/blob/master/examples/chat/client.go).
+The code for the `Client` type is in [client.go](https://github.com/gorilla/websocket/blob/main/examples/chat/client.go).
 
 The `serveWs` function is registered by the application's `main` function as
 an HTTP handler. The handler upgrades the HTTP connection to the WebSocket
@@ -85,7 +85,7 @@ network.
 
 ## Frontend
 
-The frontend code is in [home.html](https://github.com/gorilla/websocket/blob/master/examples/chat/home.html).
+The frontend code is in [home.html](https://github.com/gorilla/websocket/blob/main/examples/chat/home.html).
 
 On document load, the script checks for websocket functionality in the browser.
 If websocket functionality is available, then the script opens a connection to