README for main repo

[zhovner]

We need to make a proper README for flipperone-linux-build-scripts repo:

• Repos structure
• Automated builds
• How to build image manually
• How to contribute

[zhovner]

Started here https://github.com/flipperdevices/flipperone-linux-build-scripts/tree/zhovner/readme

[dinxsh]

I noticed PR #27 is the new README in progress. I've been building this repo on Windows 11 / Ubuntu 24.04 WSL2 and hit all the common failure modes, so I have tested content ready if it's useful to fold into the new README:

• Troubleshooting section: 7 confirmed errors with exact fixes (binfmt_misc, IMG_OUT absolute path, fallocate on NTFS, fakemachine check, IMGSIZE mismatch, cp EIO on loop-device files, no space left)
• WSL2 build path: full working script with binfmt_misc setup, loop device nodes, kpartx daemon, and the three script patches needed
• Checkpoint/reuse note: explains how to skip build-rootfs-img.sh on retries

I can contribute this as a PR targeting the zhovner/readme branch rather than adding to the current dev README. Happy to adjust format/length to match whatever structure you have in mind for #27. Let me know if this is useful.