Fixes to agent docs pt2 (#629)

Author: vishalshenoy

docs/tutorials/build-code-agent.mdx

@@ -32,7 +32,6 @@ The agent has access to powerful code viewing and manipulation tools powered by
 - `DeleteFileTool`: Delete files
 - `RenameFileTool`: Rename files
 - `EditFileTool`: Edit files 
-- `MoveSymbolTool`: Move symbols between files with import handling
 
 
 
@@ -68,6 +67,8 @@ agent = CodeAgent(
 )
 ```
 
+<Note>If using a non-default model provider, make sure to set the appropriate API key (e.g., `OPENAI_API_KEY` for OpenAI models) in your env.</Note>
+
 # Available Tools
 
 The agent comes with a comprehensive set of tools for code analysis and manipulation. Here are some key tools:
@@ -179,5 +180,5 @@ class CustomCodeTool(BaseTool):
 
 # Add custom tool to agent
 tools.append(CustomCodeTool())
-agent = CodebaseAgent(codebase, tools=tools, model_name="gpt-4o")
+agent = CodebaseAgent(codebase, tools=tools, model_name="claude-3-5-sonnet-latest")
 ```

src/codegen/extensions/langchain/tools.py

@@ -255,6 +255,7 @@ def _run(
         return result.render()
 
 
+# Note: a large file is over 300 lines. Please specify a range larger than the edit you want to make.
 _SEMANTIC_EDIT_BRIEF = """Tool for file editing via an LLM delegate. Describe the changes you want to make and an expert will apply them to the file.
 
 Specify the changes you want to make in the edit_content field, with helpful comments, like so: