Fixed 1 missing line in getting_started.md (#2107)

Seems like a copy paste error. The very next example does have this
line.

Please tell me if I missed something in the process and should have
created an issue or something first!

docs/getting_started/getting_started.md

@@ -355,13 +355,15 @@ Similar to LLMs, you can make use of templating by using a `MessagePromptTemplat
 For convience, there is a `from_template` method exposed on the template. If you were to use this template, this is what it would look like:
 
 ```python
+from langchain.chat_models import ChatOpenAI
 from langchain.prompts.chat import (
     ChatPromptTemplate,
     SystemMessagePromptTemplate,
-    AIMessagePromptTemplate,
     HumanMessagePromptTemplate,
 )
 
+chat = ChatOpenAI(temperature=0)
+
 template="You are a helpful assistant that translates {input_language} to {output_language}."
 system_message_prompt = SystemMessagePromptTemplate.from_template(template)
 human_template="{text}"
@@ -380,11 +382,10 @@ The `LLMChain` discussed in the above section can be used with chat models as we
 
 ```python
 from langchain.chat_models import ChatOpenAI
-from langchain import PromptTemplate, LLMChain
+from langchain import LLMChain
 from langchain.prompts.chat import (
     ChatPromptTemplate,
     SystemMessagePromptTemplate,
-    AIMessagePromptTemplate,
     HumanMessagePromptTemplate,
 )