readme: add sample & contributions section

Author: letmaik

README.md

@@ -2,6 +2,21 @@
 
 NOTE: This package is a work-in-progress. No support is provided, use at own risk.
 
+## Usage
+
+```py
+import pyvirtualcam
+import numpy as np
+
+with pyvirtualcam.Camera(width=1280, height=720, fps=30) as cam:
+    while True:
+        frame = np.zeros((cam.height, cam.width, 4), np.uint8) # RGBA
+        frame[:,:,:3] = cam.frames_sent % 255 # grayscale animation
+        frame[:,:,3] = 255
+        cam.send(frame)
+        cam.sleep_until_next_frame()
+```
+
 ## Installation
 
 This package is Windows-only for now. Binary wheels are provided on PyPI.
@@ -11,3 +26,11 @@ pip install pyvirtualcam
 ```
 
 The package uses [obs-virtual-cam](https://github.com/Fenrirthviti/obs-virtual-cam/releases) which has to be installed separately. Note that the obs-virtual-cam installer assumes an OBS Studio installation and will fail otherwise. You can also download and extract the obs-virtual-cam zip package directly without installing OBS Studio. After unzipping, simply run `regsvr32 /n /i:1 "obs-virtualcam\bin\32bit\obs-virtualsource.dll"` from an elevated command prompt to install the virtual camera device. Use `regsvr32 /u "obs-virtualcam\bin\32bit\obs-virtualsource.dll"` to uninstall it again.
+
+## Contributions
+
+The most useful contributions would be to add support for macOS or Linux.
+
+Similar to Windows, it may be possible in macOS to piggyback on https://github.com/johnboiles/obs-mac-virtualcam.
+
+For Linux, it seems like https://github.com/umlaeute/v4l2loopback is the right dependency. Code from https://github.com/CatxFish/obs-v4l2sink may be useful as inspiration on how to send frames to the loopback device.

samples/simple.py

@@ -0,0 +1,12 @@
+# This script is the sample from the README.
+
+import pyvirtualcam
+import numpy as np
+
+with pyvirtualcam.Camera(width=1280, height=720, fps=20, print_fps=True) as cam:
+    while True:
+        frame = np.zeros((cam.height, cam.width, 4), np.uint8) # RGBA
+        frame[:,:,:3] = cam.frames_sent % 255 # grayscale animation
+        frame[:,:,3] = 255
+        cam.send(frame)
+        cam.sleep_until_next_frame()