doc: Update README with new build and install instructions.

README.md

@@ -166,11 +166,19 @@ INSTALLING filtergen
 ====================
 
 Installing filtergen is easy.  If you don't find it easy, that's a bug.  Send
-bug reports to jaq@spacepants.org.
+bug reports here in GitHub.
+
+filtergen's build system uses [`bazel`](http://bazel.build), rather than the GNU autotools or a custom
+Makefile.  To build and install, ensure you have `bazel` or `bazelisk` installed,
+installed, and type `bazel run //:install --DESTDIR=path-to-install`.
+
+The test suite used [`DejaGNU`](https://www.gnu.org/software/dejagnu/) which is installed by `bazel`, but the system needs TCL `expect` installed.
+
+```
+sudo apt install expect
+```
+
+should be sufficient in order to run `bazel test //...`
+
 
-If you're on a Red Hat-like RPM-based system, you should be able just to run
-"rpm -ta" on the tarball.  Debian users can fetch released versions from `apt`.
 
-filtergen's build system uses SCons, rather than the GNU autotools or a custom
-Makefile.  To build and install, ensure you have SCons, gcc, flex, and bison
-installed, and type "scons install".