[Workers] Add Error 501 Not Implemented documentation

src/content/docs/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-501.mdx

@@ -0,0 +1,18 @@
+---
+pcx_content_type: troubleshooting
+title: Error 501
+source: null
+---
+
+## Error 501: not implemented
+
+Cloudflare Workers returns a `501` error when a request uses an HTTP method that is not supported by the Workers Runtime.
+
+### Common causes
+
+- A client sent a request to a Workers script using a custom or non-standard HTTP method (methods outside of `GET`, `POST`, `PUT`, etc.).
+- A typo in the HTTP method (for example, `POT` instead of `POST`).
+
+### Resolution
+
+- Update the client to use a valid, standard [HTTP request method](https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods).

src/content/docs/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/index.mdx

@@ -53,6 +53,10 @@ Log explorer [allows to build queries](/log-explorer/log-search/) filtering for
 
 For a complete description of this error refer to the [Error 500](/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-500/) page.
 
+## Error 501: not implemented
+
+For a complete description of this error refer to the [Error 501](/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-501/) page.
+
 ## Error 502 bad gateway or error 504 gateway timeout
 
 For a complete description of this error refer to the [Error 502/504](/support/troubleshooting/http-status-codes/cloudflare-5xx-errors/error-502-504/) page.