README: document bootstrap/build steps

The generated autotools files are not tracked, so a fresh clone must run
autogen.sh before configure. State that and the build dependencies.

README

@@ -53,3 +53,15 @@ the code and documentation are to avoid confusion by users, not to avoid
 proper attribution. Reiserfsprogs has been maintained by the ReiserFS
 development community for some time and can be reached at
 reiserfs-devel@vger.kernel.org.
+
+[BUILDING]
+
+The generated autotools files (configure, Makefile.in, ...) are not kept in
+the repository. After a fresh clone, bootstrap them first:
+
+	./autogen.sh
+	./configure
+	make
+
+Build dependencies: a C compiler, autoconf, automake, libtool, pkg-config,
+libcom_err (com_err development files) and, optionally, libuuid.