Clarify missing files error message.
diff --git a/gpt_engineer/db.py b/gpt_engineer/db.py
index c3db67c103..0d7e64eed6 100644
--- a/gpt_engineer/db.py
+++ b/gpt_engineer/db.py
@@ -18,7 +18,7 @@ def __getitem__(self, key):
         full_path = self.path / key
 
         if not full_path.is_file():
-            raise KeyError(key)
+            raise KeyError(f"File '{key}' could not be found in '{self.path}'")
         with full_path.open("r", encoding="utf-8") as f:
             return f.read()
 

What do you think in clarify the error message when missing a file? I had trouble understanding what was wrong when I missed some files such as the prompt "main_prompt" or the "feedback" file. 

This commit changes the error message to help the user understand what needs to be done to execute the program correctly. 

ie. When missing the "feedback" file, the error before this commit was:

`KeyError: 'feedback'`

and now is:

`KeyError: "File 'feedback' could not be found in 'C:\\xxx\\xxxx\\gpt-engineer\\projects\\test'"`

As shows figure above:

![cmd_5MnGbGSMbT](https://github.com/AntonOsika/gpt-engineer/assets/11357793/cc3a579e-1bb5-4904-9c98-48e897f2636d)
