Add more documentation for mitmproxy

mitmproxy/REWADME.md

@@ -1,3 +1,26 @@
 # mitmproxy script
 
 This folder includes a [mitmproxy](https://mitmproxy.org/) [addon](https://docs.mitmproxy.org/stable/addons-overview/) which can replace the OnlyOffice client in any CryptPad instance with files served from the local disk.
+
+## How to install and setup mitmproxy
+
+### 1) Install [mitmproxy](https://mitmproxy.org/)
+
+### 2) Create a dedicated profile for you browser
+
+Since we will weaken you browsers security with a self signed certificate, I suggest that you created a dedicated browser profile you use together with mitmproxy. When using Firefox, you can call `firefox -P` and create a new profile.
+
+
+### 3) Setup your borwser
+
+Start `mitmproxy` from a terminal and configure your browser to use http://localhost:8080 as your proxy for the HTTP and HTTPS protocol.
+
+After that open http://mitm.it/ and download the cenerated certificate for your browser and read the instructions on how to install it.
+
+### 4) Check you setup
+
+Now you should be able to browse the internet and all requests should apper in the terminal where `mitmproxy` is running.
+
+## How to use mitmproxy to replace the OnlyOffice client with a local copy
+
+TODO