docs: move documentation into the GitHub wiki (#21)

- Rewrite README.md as a slim landing page pointing to the wiki
- Remove the doc/ directory; its pages now live in the GitHub wiki
- Repoint the in-code doc/ references to their wiki URLs in the workflow templates and the workflows help text
- Replace the doc/INSTALL.md example in img/README.md with a generic app README
- Add .gitattributes to normalise line endings to LF

Signed-off-by: ernolf <raphael.gradenwitz@googlemail.com>

Author: ernolf

.gitattributes

@@ -0,0 +1,7 @@
+# SPDX-FileCopyrightText: 2026 [ernolf] Raphael Gradenwitz <raphael.gradenwitz@googlemail.com>
+# SPDX-License-Identifier: MIT
+
+# Store and check out every text file with LF, regardless of a contributor's
+# core.autocrlf setting, so line endings never leak into a diff. Binary files
+# are detected by text=auto and left untouched.
+* text=auto eol=lf