Add section/sentence to readme regarding windows installation

[lursyy]

I had to experiment a bit to get this to compile under Windows x64. I suggest adding a few lines to the readme, but would like someone to verify that the instructions work, because I am not 100% sure if these steps were all I did.

My steps:

• (install rust via rustup)
• Install vcpkg and run integrate install
• vcpkg install openssl:x64-windows-static-md
• vcpkg install sqlite3[fts5]:x64-windows-static-md (installs sqlite3 and the fts5 extension, which is required)
• (cargo install signal-backup-decode)

Finding the correct openssl and sqlite packages was a bit tedious (with my limited knowledge), as I did not know about -md and [fts5]. Maybe just a pointer towards that would be nice in the readme?

[Tracy58468]

I just installed everything and I had to:

1. Install Visual Studio with Desktop Development with C++ enabled.
2. Install Rust.
3. Install vcpkg using the instructions I found here: https://devblogs.microsoft.com/cppblog/vcpkg-a-tool-to-acquire-and-build-c-open-source-libraries-on-windows/, except that since I have moved my user folders to the D drive, I had to search down the correct BAT file to execute.

But now I'm stuck at lursyy's second step. I'm running this in Git Bash, and I get "bash: integrate: command not found".

I'm not sure what to do next.

ETA: I'm running Windows 10.

[lursyy]

I am pretty sure I did this in Powershell, can you try it there? I am not sure how Git Bash interacts with Windows in such a case...