added readme

readme.md

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+### Usage
+
+1. Prepare & install
+    1. ```brew tap osx-cross/avr```
+    2. ```brew install avr-gcc``` 
+    3. ```brew install avrdude``` 
+    4. OPTIONAL: GUI for avrdude (to easily read and set fuses):
+        1. Install AVRFuses for Mac from http://vonnieda.org/software/avrfuses and open it
+        2. Point AVRFuses to your avrdude installation:
+            1. Get path via command line ```$ which avrdude```
+        3. Connect your USPasp to your Arduino and plug it into your Mac.
+        4. Chose the usbasp in the programmer dropdown.
+        5. Choose the usb port in AVRFuses. In my case it was just ```usb```. Close Settings window.
+        6. Click on „Autodetect“ to verify that everything works as expected. Now you can read and set Fuses.
+2. Setup project in vscode with make
+    1. Install c/c++ extension via marketplace
+    2. Download https://git.timovolkmann.de/tvolkmann/avr-vsc-c-demo for sample project. Make sure that paths in ```.vscode/c_cpp_properties.json``` are correct.
+    3. Enter project directory and build with ```$ make all``` 
+    4. Flash to Arduino with ```$ make flash```
+
+### Helpful resources
+
+- https://github.com/tilaktilak/atmega328P/blob/master/makefile
+- tbd