Merge branch 'bochecha/cache-size' into 'master'

data/userconfig.yaml: Document the cache.quota setting

See merge request !833

buildstream/data/userconfig.yaml

@@ -26,8 +26,13 @@ logdir: ${XDG_CACHE_HOME}/buildstream/logs
 #    Cache
 #
 cache:
-  # Size of the artifact cache - BuildStream will attempt to keep the
+  # Size of the artifact cache in bytes - BuildStream will attempt to keep the
   # artifact cache within this size.
+  # If the value is suffixed with K, M, G or T, the specified memory size is
+  # parsed as Kilobytes, Megabytes, Gigabytes, or Terabytes (with the base
+  # 1024), respectively.
+  # Alternatively, a percentage value may be specified, which is taken relative
+  # to the isize of the file system containing the cache.
   quota: infinity
 
 #