New docs

docs/reference-and-help/faq.md

@@ -1,2 +1,34 @@
 # FAQ
 
+## What commands are available?
+
+`new`, `init`, `build`, `run`, `clean`, `--help`, `--version`, `--update`.
+
+## Is `dcr.toml` mandatory?
+
+Yes, for `build`, `run`, and `clean`.
+
+## What source files are compiled?
+
+DCR scans `src/` recursively:
+
+- for C: `*.c`
+- for C++: `*.cpp`, `*.cxx`, `*.cc`
+
+## Can I switch compiler?
+
+Yes. Set `build.compiler` in `dcr.toml` (for example `gcc`, `clang`, `cl`, `clang-cl`).
+
+## How does incremental rebuild work?
+
+It compares source file mtime with object file mtime. Header dependency tracking is not implemented yet.
+
+## What does `dcr run` do if build fails?
+
+It tries to run an existing binary from the selected profile; if none exists, it reports an error.
+
+## How do I update DCR?
+
+Use `dcr --update` for non-package-managed installs.
+
+If installed through pacman/AUR, update via package manager.