Document local action cache

site/docs/remote-caching.md

@@ -26,6 +26,7 @@ make builds significantly faster.
     * [Read only from the remote cache](#read-only-from-the-remote-cache)
     * [Exclude specific targets from using the remote cache](#exclude-specific-targets-from-using-the-remote-cache)
     * [Delete content from the remote cache](#delete-content-from-the-remote-cache)
+* [Local action cache](#local-action-cache)
 * [Known Issues](#known-issues)
 * [External Links](#external-links)
 * [Bazel remote execution (in development)](#bazel-remote-execution-in-development)
@@ -306,6 +307,31 @@ You may want to delete content from the cache to:
 * Create a clean cache after a cache was poisoned
 * Reduce the amount of storage used by deleting old outputs
 
+## Local action cache
+
+Bazel supports directory based action cache. It may be very useful, when
+working on multiple branches or multiple workspaces of the same project.
+It's also supported to provide user specific directory cache location, so
+that the local cache activation can be configured in project wide
+configuration file and committed into project repository. To activate the
+local action cache, add this line to your `tools/bazel.rc` file:
+
+```
+build --local_disk_cache=~/.gerrit/bazel-cache/cas
+```
+
+To have cache hits across different workspaces, additional option should be
+used to prevent Bazel to forward `PATH`, `LD_LIBRARY_PATH`, and `TMPDIR` env
+variables to all actions:
+
+```
+build --experimental_strict_action_env
+```
+
+This option should be activated per default, by providing some sane cache
+location, like `~/.bazel/cas` or similar, but currently, one feature is
+still missing to allow to specify an upper bound on the cache directory.
+
 ## Known issues
 
 **Input file modification during a Build**