manual: contributing: move and expand autobuild section

This patch moves the section about autobuild fixing up, and expands it with
more details about what autobuilds are, and how you can help with it.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Acked-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

docs/manual/contribute.txt

@@ -33,6 +33,52 @@ help in reproducing, analyzing and fixing reported bugs is more than
 welcome. Don't hesitate to add a comment to bug reports reporting your
 findings, even if you don't yet see the full picture.
 
+Analyzing and fixing autobuild failures
+---------------------------------------
+
+The Buildroot autobuilders are a set of build machines that continuously
+run Buildroot builds based on random configurations. This is done for
+all architectures supported by Buildroot, with various toolchains, and
+with a random selection of packages. With the large commit activity on
+Buildroot, these autobuilders are a great help in detecting problems
+very early after commit.
+
+All build results are available at http://autobuild.buildroot.org[],
+statistics are at http://autobuild.buildroot.org/stats.php[]. Every day,
+an overview of all failed packages is sent to the mailing list.
+
+Detecting problems is great, but obviously these problems have to be
+fixed as well. Your contribution is very welcome here! There are
+basically two things that can be done:
+
+- Analyzing the problems. The daily summary mails do not contain details
+  about the actual failures: in order to see what's going on you have to
+  open the build log and check the last output. Having someone doing
+  this for all packages in the mail is very useful for other developers,
+  as they can make a quick initial analysis based on this output alone.
+
+- Fixing a problem. When fixing autobuild failures, you should follow
+  these steps:
+  . Check if you can reproduce the problem by building with the same
+    configuration. You can do this manually, or use the
+    http://git.buildroot.org/buildroot-test/tree/utils/br-reproduce-build[br-reproduce-build]
+    script that will automatically clone a Buildroot git repository,
+    checkout the correct revision, download and set the right
+    configuration, and start the build.
+  . Analyze the problem and create a fix.
+  . Verify that the problem is really fixed by starting from a clean
+    Buildroot tree and only applying your fix.
+  . Send the fix to the Buildroot mailing list (see
+    xref:submitting-patches[]). In case you created a patch against the
+    package sources, you should also send the patch upstream so that the
+    problem will be fixed in a later release, and the patch in Buildroot
+    can be removed.
+    In the commit message of a patch fixing an autobuild failure, add a
+    reference to the build result directory, as follows:
+---------------------
+Fixes http://autobuild.buildroot.org/results/51000a9d4656afe9e0ea6f07b9f8ed374c2e4069
+---------------------
+
 [[submitting-patches]]
 Submitting patches
 ------------------
@@ -210,23 +256,6 @@ Buildroot's Patchwork website can be used to pull in patches for testing
 purposes. Please see xref:apply-patches-patchwork[] for more
 information on using Buildroot's Patchwork website to apply patches.
 
-Autobuild
----------
-
-The Buildroot community is currently setting up automatic builds in
-order to test more and more configurations. All build results are
-available at http://autobuild.buildroot.org[]
-
-A good way to contribute is by fixing broken builds.
-
-In the commit message of a patch fixing an _autobuild_, add a
-reference to the _build result directory_ (the +dir+ link in the _data
-column_):
-
----------------------
-Fixes http://autobuild.buildroot.org/results/51000a9d4656afe9e0ea6f07b9f8ed374c2e4069
----------------------
-
 [[reporting-bugs]]
 Reporting issues/bugs, get help
 -------------------------------