doc: make build steps more prominent

Author: coolaj86

README.md

@@ -10,7 +10,7 @@ https://www.dash.org
 For an immediately usable, binary version of the Dash Core software, see
 https://www.dash.org/downloads/.
 
-Further information about Dash Core is available in the [doc folder](/doc).
+Further information about Dash Core is available in [./doc/](/doc).
 
 What is Dash?
 -------------
@@ -43,6 +43,19 @@ completely stable.
 The contribution workflow is described in [CONTRIBUTING.md](CONTRIBUTING.md)
 and useful hints for developers can be found in [doc/developer-notes.md](doc/developer-notes.md).
 
+Build / Compile from Source
+---------------------------
+
+The `./configure`, `make`, and `cmake` steps, as well as build dependencies, are in [./doc/](/doc) as well:
+
+- **Linux**: [./doc/build-unix.md](/doc/build-unix.md) \
+  Ubuntu, Debian, Fedora, Arch, and others
+- **macOS**: [./doc/build-osx.md](/doc/build-osx.md)
+- **Windows**: [./doc/build-windows.md](/doc/build-windows.md)
+- **OpenBSD**: [./doc/build-openbsd.md](/doc/build-openbsd.md)
+- **FreeBSD**: [./doc/build-freebsd.md](/doc/build-freebsd.md)
+- **NetBSD**: [./doc/build-netbsd.md](/doc/build-netbsd.md)
+
 Testing
 -------