site: build instructions: mention where to find binaries.

Documenting where to find binaries built with 'make release' helps
users trying to build GNU Boot for the first time, especially if
something goes wrong.

It is also extremely useful for contributors writing release scripts
as this avoid needing to build a complete release just to find out the
name and location of released files.

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>
Acked-by: Adrien 'neox' Bourmault <neox@gnu.org>

site/docs/build/index.md

@@ -85,14 +85,32 @@ command instead:
 
     sudo make install-dependencies-pureos-10
 
-When this is done you can build all the GNU Boot images with the
+
-following command (this uses the Makefile):
+You can then build everything with this command:
+
+    make release
+
+When the compilation ends this should have created images for all the
+computers supported by GNU Boot in release/roms/. For instance if you
+are building GNU Boot 0.1 RC1 the image for the Thinkpad X60 will be
+in release/roms/gnuboot-0.1-rc1_x60.tar.xz.
+
+It will also create an archive of all the upstream source code used to
+build GNU Boot but without any nonfree software in it. For GNU Boot
+0.1 RC1 the archive will be in release/gnuboot-0.1-rc1_src.tar.xz.
+
+If you use git revisions that are not releases you might instead end
+up with something like '0.2-10-g1234abcdefg' instead of '0.1-rc1'
+inside the file names. For the curious, that part of the filename is
+computed with the 'git describe HEAD' command.
+
+If instead you only want to build all the images and not build an
+archive of the source code you can use this command:
 
     make
 
-This single command will build ROM images for *every* computer
+If you only wish to build a limited set of images, you can use the
-supported by GNU Boot. If you only wish to build a limited set, you
+build script directly:
-can use the build script directly:
 
     ./build boot roms x200_8mb
 
@@ -115,9 +133,6 @@ To clean your `crossgcc` builds:
 
     make crossgcc-clean
 
-To build release archives:
-
-    make release
 
 Build without using GNU Make
 ============================