📝 Add docs for Form data

docs/tutorial/form-data.md

@@ -0,0 +1,40 @@
+When you need to receive form data instead of JSON, you can use `Form`.
+
+## Import Form
+
+Import `Form` from `fastapi`:
+
+```Python hl_lines="1"
+{!./tutorial/src/form-data/tutorial001.py!}
+```
+
+## Define Form parameters
+
+Create form parameters the same way you would for `Body`:
+
+```Python hl_lines="7"
+{!./tutorial/src/form-data/tutorial001.py!}
+```
+
+For example, for one of the ways the OAuth2 specification can be used (called "password flow") it is required to send a `username` and `password` fields as form data.
+
+The <abbr title="specification">spec</abbr> requires the fields to be specifically named `username` and `password`, and to be sent as form data, not JSON.
+
+With `Form` you can declare the same metadata and validation as with `Body` (and `Query`, `Path`, `Cookie`).
+
+!!! info
+    `Form` is a class that inherits directly from `Body`.
+
+!!! info
+    To declare form bodies, you need to use `Form`, because otherwise the parameters would be interpreted as query parameteres or body (JSON) parameters.
+
+## "Form Data"? 
+
+"Form data" is the way HTML forms (`<form></form>`) send the data to the server.
+
+!!! note "Technical Details"
+    Data from forms is normally encoded using the "media type" `application/x-www-form-urlencoded`. To read more about it head to the <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST" target="_blank"><abbr title="Mozilla Developer Network">MDN</abbr> web docs for <code>POST</code></a>.
+
+## Recap
+
+Use `Form` to declare form data input parameters.

docs/tutorial/src/form-data/tutorial001.py

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+from fastapi import FastAPI, Form
+
+app = FastAPI()
+
+
+@app.post("/login/")
+async def login(*, username: str = Form(...), password: str = Form(...)):
+    return {"username": username}

mkdocs.yml

@@ -31,6 +31,7 @@ nav:
         - Header Parameters: 'tutorial/header-params.md'
         - Response Model: 'tutorial/response-model.md'
         - Extra Models: 'tutorial/extra-models.md'
+        - Form Data: 'tutorial/form-data.md'
     - Concurrency and async / await: 'async.md'
     - Deployment: 'deployment.md'