Explain how to fix 'httpd_parse: header too long'

Because this is the 'simple' server example, it is probably where users will start out to understand the HTTP Server API; and also where they might come if they are having problems.
So I think it is useful to explain to users what to do if they see "httpd_parse: parse_block: request URI/header too long", which can easily happen if they submit a POST from an HTML form (for example). That certainly would have helped me!

Merges https://github.com/espressif/esp-idf/pull/6547

Signed-off-by: Shubham Kulkarni <shubham.kulkarni@espressif.com>

examples/protocols/http_server/simple/README.md

@@ -21,4 +21,6 @@ The Example consists of HTTPD server demo with demostration of URI handling :
             3. "curl -X PUT -d "0" 192.168.43.130:80/ctrl" - disable /hello and /echo handlers
             4. "curl -X PUT -d "1" 192.168.43.130:80/ctrl" -  enable /hello and /echo handlers
             
+* If the server log shows "httpd_parse: parse_block: request URI/header too long", especially when handling POST requests, then you probably need to increase HTTPD_MAX_REQ_HDR_LEN, which you can find in the project configuration menu (`idf.py menuconfig`): Component config -> HTTP Server -> Max HTTP Request Header Length
+
 See the README.md file in the upper level 'examples' directory for more information about examples.