Docs update: Redirect paths with parentheses (#24062)

It took me quite a while to understand that in order to redirect from `/english(default)/:path` to `/en-us/:path`, I have to escape the parentheses in the source with double backslashes so I thought I'd suggest it as a small doc update.


## Documentation / Examples

- [x] Make sure the linting passes

docs/api-reference/next.config.js/headers.md

@@ -154,6 +154,23 @@ module.exports = {
 }
 ```
 
+The following characters `(`, `)`, `{`, `}`, `:`, `*`, `+`, `?` are used for regex path matching, so when used in the `source` as non-special values they must be escaped by adding `\\` before them:
+
+```js
+module.exports = {
+  async redirects() {
+    return [
+      {
+        // this will match `/english(default)/something` being requested
+        source: '/english\\(default\\)/:slug',
+        destination: '/en-us/:slug',
+        permanent: false,
+      },
+    ]
+  },
+}
+```
+
 ## Header, Cookie, and Query Matching
 
 Note: this feature is still experimental and not covered by semver and is to be used at your own risk until it is made stable.

docs/api-reference/next.config.js/redirects.md

@@ -82,7 +82,7 @@ module.exports = {
 
 ### Regex Path Matching
 
-To match a regex path you can wrap the regex in parenthesis after a parameter, for example `/post/:slug(\\d{1,})` will match `/post/123` but not `/post/abc`:
+To match a regex path you can wrap the regex in parentheses after a parameter, for example `/post/:slug(\\d{1,})` will match `/post/123` but not `/post/abc`:
 
 ```js
 module.exports = {
@@ -98,6 +98,23 @@ module.exports = {
 }
 ```
 
+The following characters `(`, `)`, `{`, `}`, `:`, `*`, `+`, `?` are used for regex path matching, so when used in the `source` as non-special values they must be escaped by adding `\\` before them:
+
+```js
+module.exports = {
+  async redirects() {
+    return [
+      {
+        // this will match `/english(default)/something` being requested
+        source: '/english\\(default\\)/:slug',
+        destination: '/en-us/:slug',
+        permanent: false,
+      },
+    ]
+  },
+}
+```
+
 ## Header, Cookie, and Query Matching
 
 Note: this feature is still experimental and not covered by semver and is to be used at your own risk until it is made stable.

docs/api-reference/next.config.js/rewrites.md

@@ -178,6 +178,23 @@ module.exports = {
 }
 ```
 
+The following characters `(`, `)`, `{`, `}`, `:`, `*`, `+`, `?` are used for regex path matching, so when used in the `source` as non-special values they must be escaped by adding `\\` before them:
+
+```js
+module.exports = {
+  async redirects() {
+    return [
+      {
+        // this will match `/english(default)/something` being requested
+        source: '/english\\(default\\)/:slug',
+        destination: '/en-us/:slug',
+        permanent: false,
+      },
+    ]
+  },
+}
+```
+
 ## Header, Cookie, and Query Matching
 
 Note: this feature is still experimental and not covered by semver and is to be used at your own risk until it is made stable.