Add documentation for build pruning

admin_guide/pruning_resources.adoc

@@ -144,6 +144,12 @@ $ oadm prune builds --orphans --keep-complete=5 --keep-failed=1 \
     --keep-younger-than=60m --confirm
 ----
 
+[NOTE]
+====
+Developers can enable xref:../../dev_guide/advanced_build_operations.adoc#build-pruning[automatic build pruning]
+by modifying their build configuration.
+====
+
 [[pruning-images]]
 
 == Pruning Images

dev_guide/builds/advanced_build_operations.adoc

@@ -262,3 +262,37 @@ whenever the first build is run and produces a new image with the binary
 artifact, the second build is automatically triggered to produce a runtime image
 that contains that artifact. Therefore, both builds behave as a single build
 with two stages.
+
+[[build-pruning]]
+== Build Pruning
+
+By default, builds that have completed their lifecycle are persisted indefinitely.
+You can limit the number of previous builds that are retained by supplying a positive
+integer value for `successfulBuildsHistoryLimit` or `failedBuildsHistoryLimit`
+as shown in the below sample build configuration.
+
+[source,yaml]
+----
+apiVersion: "v1"
+kind: "BuildConfig"
+metadata:
+  name: "sample-build"
+spec:
+  successfulBuildsHistoryLimit: 2 <1>
+  failedBuildsHistoryLimit: 2 <2>
+----
+<1> `successfulBuildsHistoryLimit` will retain up to 2 builds with a status of `completed`
+<2> `failedBuildsHistoryLimit` will retain up to 2 builds with a status of `failed`, `cancelled`, or `error`
+
+Build pruning is triggered by the following actions:
+
+ - the build configuration is updated
+ - a build completes its lifecycle
+
+Builds are sorted by their creation timestamp with the oldest builds being pruned first.
+
+[NOTE]
+====
+Administrators can manually prune builds using the xref:../../admin_guide/pruning_resources.adoc#pruning-builds[oadm object pruning command].
+====
+