filled docs with basics

README.md

@@ -1,7 +1,29 @@
-## GUI tool for secure file transfer
+<div align="center" style="text-align:center">
+    <picture>
+        <source media="(prefers-color-scheme: dark)" srcset="https://github.com/17ms/contego/blob/master/docs/contego-dark.png">
+        <source media="(prefers-color-scheme: light)" srcset="https://github.com/17ms/contego/blob/master/docs/contego-light.png">
+    </picture>
+</div>
 
 <p align="left">
 <a href="https://github.com/17ms/contego/actions/workflows/ci.yml"><img src="https://img.shields.io/github/actions/workflow/status/17ms/contego/ci.yml?branch=main"></a>
 <a href="https://github.com/17ms/contego/tags"><img src="https://img.shields.io/github/v/tag/17ms/contego"></a>
 <a href="https://opensource.org/licenses/MIT"><img src="https://img.shields.io/github/license/17ms/contego"></a>
 </p>
+
+## Cryptographic specifications
+
+The initial key exchange is performed with elliptic-curve Diffie-Hellman. General data exchange is encrypted with AES-GCM. During regular communication payloads are Base64 encoded before being encrypted to prevent delimiter conflicts. SHA-256 hashes of files are compared to ensure data integrity.
+
+## Cellular networks
+
+Most cellular ISP's tend to block port forwarding on CGNAT level, which makes it impossible to create inbound connections to such network without a VPN. Luckily many consumer VPNs and self-hosted solutions make port forwarding a trivial task. This is the main reason why the client must fetch information about the public IP from an external service (https://ipinfo.io/ip for IPV4 and https://ipv6.icanhazip.com for IPV6). 
+
+## Usage
+
+Work in progress. Will be completed when the current release is finished.
+
+```shell
+cargo build --release
+./target/release/contego
+```