Use !include to read text files into context for the assistant (#98)

Read text files into assistant context with:

```yaml
default_assistant: dev
markdown: True
openai_api_key: <openai_api_key>
assistants:
  pirate:
    model: gpt-4
    temperature: 1.0
    messages:
      - { role: system, content: !include "pirate.txt" }
```

README.md

@@ -181,6 +181,23 @@ $ gpt pirate
 Ahoy, matey! What be bringing ye to these here waters? Be it treasure or adventure ye seek, we be sailing the high seas together. Ready yer map and compass, for we have a long voyage ahead!
 ```
 
+### Read other context to the assistant with !include
+
+You can read in files to the assistant's context with !include <file_path>.
+
+```yaml
+default_assistant: dev
+markdown: True
+openai_api_key: <openai_api_key>
+assistants:
+  pirate:
+    model: gpt-4
+    temperature: 1.0
+    messages:
+      - { role: system, content: !include "pirate.txt" }
+```
+
+
 ### Customize OpenAI API URL
 
 If you are using other models compatible with the OpenAI Python SDK, you can configure them by modifying the `openai_base_url` setting in the config file or using the `OPENAI_BASE_URL` environment variable .

gptcli/config.py

@@ -1,12 +1,12 @@
 import os
 from typing import Dict, List, Optional
-from attr import dataclass
+
 import yaml
+from attr import dataclass
 
 from gptcli.assistant import AssistantConfig
 from gptcli.providers.llama import LLaMAModelConfig
 
-
 CONFIG_FILE_PATHS = [
     os.path.join(os.path.expanduser("~"), ".config", "gpt-cli", "gpt.yml"),
     os.path.join(os.path.expanduser("~"), ".gptrc"),
@@ -38,9 +38,24 @@ def choose_config_file(paths: List[str]) -> str:
     return ""
 
 
+# Custom YAML Loader with !include support
+class CustomLoader(yaml.SafeLoader):
+    pass
+
+
+def include_constructor(loader, node):
+    # Get the file path from the node
+    file_path = loader.construct_scalar(node)
+    # Read and return the content of the included file
+    with open(file_path, "r") as include_file:
+        return include_file.read()
+
+
+# Register the !include constructor
+CustomLoader.add_constructor("!include", include_constructor)
+
+
 def read_yaml_config(file_path: str) -> GptCliConfig:
     with open(file_path, "r") as file:
-        config = yaml.safe_load(file)
-        return GptCliConfig(
-            **config,
-        )
+        config = yaml.load(file, Loader=CustomLoader)
+        return GptCliConfig(**config)