Update Getting Started page of Prompt Templates (#3298)

Updated `Getting Started` page of `Prompt Templates` to showcase more
features provided by the class. Might need some proof reading because
apparently English is not my first language.

docs/modules/prompts/prompt_templates/getting_started.md

@@ -23,15 +23,6 @@ from langchain import PromptTemplate
 
 template = """
 I want you to act as a naming consultant for new companies.
-
-Here are some examples of good company names:
-
-- search engine, Google
-- social media, Facebook
-- video sharing, YouTube
-
-The name should be short, catchy and easy to remember.
-
 What is a good name for a company that makes {product}?
 """
 
@@ -39,6 +30,9 @@ prompt = PromptTemplate(
     input_variables=["product"],
     template=template,
 )
+prompt.format(product="colorful socks")
+# -> I want you to act as a naming consultant for new companies.
+# -> What is a good name for a company that makes colorful socks?
 ```
 
 
@@ -69,30 +63,81 @@ multiple_input_prompt.format(adjective="funny", content="chickens")
 # -> "Tell me a funny joke about chickens."
 ```
 
+If you do not wish to specify `input_variables` manually, you can also create a `PromptTemplate` using `from_templates` class method. `langchain` will automatically infer the `input_variables` based on the `template` passed.
+
+```python
+template = "Tell me a {adjective} joke about {content}."
+
+prompt_template = PromptTemplate.from_template(template)
+prompt_template.input_variables
+# -> ['adjective', 'content']
+prompt_template.format(adjective="funny", content="chickens")
+# -> Tell me a funny joke about chickens.
+```
 
 You can create custom prompt templates that format the prompt in any way you want. For more information, see [Custom Prompt Templates](examples/custom_prompt_template.ipynb).
 
 
 <!-- TODO(shreya): Add link to Jinja -->
 
-:::{note}
-Currently, the template should be formatted as a Python f-string. We also support Jinja2 templates (see [Using Jinja templates](examples/custom_prompt_template.ipynb)). In the future, we will support more templating languages such as Mako.
-:::
-
-
-## Load a prompt template from LangChainHub
-
-LangChainHub contains a collection of prompts which can be loaded directly via LangChain.
+## Template formats
 
+By default, `PromptTemplate` will treat the provided template as a Python f-string. You can specify other template format through `template_format` argument:
 
 ```python
+# Make sure jinja2 is installed before running this
+
+jinja2_template = "Tell me a {{ adjective }} joke about {{ content }}"
+prompt_template = PromptTemplate.from_template(template=jinja2_template, template_format="jinja2")
+
+prompt_template.format(adjective="funny", content="chickens")
+# -> Tell me a funny joke about chickens.
+```
+
+Currently, `PromptTemplate` only supports `jinja2` and `f-string` templating format. If there is any other templating format that you would like to use, feel free to open an issue in the [Github](https://github.com/hwchase17/langchain/issues) page. 
+
+## Validate template
+
+By default, `PromptTemplate` will validate the `template` string by checking whether the `input_variables` match the variables defined in `template`. You can disable this behavior by setting `validate_template` to `False`
+
+```python
+template = "I am learning langchain because {reason}."
+
+prompt_template = PromptTemplate(template=template, 
+                                 input_variables=["reason", "foo"]) # ValueError due to extra variables
+prompt_template = PromptTemplate(template=template, 
+                                 input_variables=["reason", "foo"], 
+                                 validate_template=False) # No error
+```
+
+
+## Serialize prompt template
+
+You can save your `PromptTemplate` into a file in your local filesystem. `langchain` will automatically infer the file format through the file extension name. Currently, `langchain` supports saving template to YAML and JSON file. 
+
+```python
+prompt_template.save("awesome_prompt.json") # Save to JSON file
+```
+
+```python
+from langchain.prompts import load_prompt
+loaded_prompt = load_prompt("awesome_prompt.json")
+
+assert prompt_template == loaded_prompt
+```
+
+`langchain` also supports loading prompt template from LangChainHub, which contains a collection of useful prompts you can use in your project. You can read more about LangChainHub and the prompts available with it [here](https://github.com/hwchase17/langchain-hub).
+
+```python
+
 from langchain.prompts import load_prompt
 
 prompt = load_prompt("lc://prompts/conversation/prompt.json")
 prompt.format(history="", input="What is 1 + 1?")
 ```
 
-You can read more about LangChainHub and the prompts available with it [here](https://github.com/hwchase17/langchain-hub).
+You can learn more about serializing prompt template in [How to serialize prompts](examples/prompt_serialization.ipynb).
+
 
 ## Pass few shot examples to a prompt template