New docs

docs/dependencies-and-build/dependency-format.md

@@ -1,2 +1,26 @@
 # Dependency format
 
+Dependencies are defined in `dcr.toml` under `[dependencies]`.
+
+## Full example
+
+```toml
+[dependencies]
+fmt = { path = "./third_party/fmt", include = ["include"], lib = ["lib"], libs = ["fmt"] }
+```
+
+## Field reference
+
+- `path`: required dependency root path.
+- `include`: optional include subpaths (absolute or relative to dep root).
+- `lib`: optional library subpaths (absolute or relative to dep root).
+- `libs`: optional linker library names.
+
+## Common valid compact form
+
+```toml
+[dependencies]
+mylib = { path = "./libs/mylib" }
+```
+
+In this form DCR will try defaults for include/lib dirs and use `mylib` as the linker library name.