add mainpage image, fix bitcoin instructions

Author: blckbx

assets/images/mainpage.png

@@ -90,5 +90,5 @@ MemoryDenyWriteExecute=true
 SystemCallArchitectures=native
 
 [Install]
-WantedBy=multi-user.target" | sudo tee /etc/systemd/system/${prefix}bitcoind.service
+WantedBy=multi-user.target" | sudo tee /etc/systemd/system/bitcoind.service
 ```

bitcoind.markdown

@@ -5,6 +5,10 @@ nav_order: 1
 permalink: /
 ---
 
+<p align="center">
+    <img src="./assets/images/mainpage.png" title="main page" width="50%" />
+</p>
+
 ## A Collection of compilation snippets
 
 This is a collection of code snippets for running your own Bitcoin and Lightning node at home, empowering you with full control over your financial sovereignty without relying on third-party services. The guide details step-by-step installation instructions focused on self-compiling binaries from trusted open-source GitHub repositories, ensuring transparency, security, and customization tailored to x86/amd64 hardware and an underlying Linux OS.