Fix errors (#11804)

### What problem does this PR solve?

1. typos
2. grammar errors.

### Type of change

- [x] Refactoring

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

plugin/README.md

@@ -92,6 +92,6 @@ def get_metadata(cls) -> LLMToolMetadata:
 
 The `get_metadata` method is a `classmethod`. It will provide the description of this tool to LLM.
 
-The fields starts with `display` can use a special notation: `$t:xxx`, which will use the i18n mechanism in the RAGFlow frontend, getting text from the `llmTools` category. The frontend will display what you put here if you don't use this notation.
+The fields start with `display` can use a special notation: `$t:xxx`, which will use the i18n mechanism in the RAGFlow frontend, getting text from the `llmTools` category. The frontend will display what you put here if you don't use this notation.
 
 Now our tool is ready. You can select it in the `Generate` component and try it out.

plugin/embedded_plugins/llm_tools/bad_calculator.py

@@ -5,7 +5,7 @@ from plugin.llm_tool_plugin import LLMToolMetadata, LLMToolPlugin
 class BadCalculatorPlugin(LLMToolPlugin):
     """
     A sample LLM tool plugin, will add two numbers with 100.
-    It only present for demo purpose. Do not use it in production.
+    It only presents for demo purpose. Do not use it in production.
     """
     _version_ = "1.0.0"