Update aspect documentation to reflect aspect parameters.

RELNOTES: none
PiperOrigin-RevId: 160467549
diff --git a/site/docs/skylark/aspects.md b/site/docs/skylark/aspects.md
index 5dcaf1b..2ec6d5a 100644
--- a/site/docs/skylark/aspects.md
+++ b/site/docs/skylark/aspects.md
@@ -93,10 +93,14 @@
 specify the aspect's propagation set: a list of attributes of rules along which
 the aspect propagates.
 
-``attrs`` defines a set of attributes for aspects. Aspects are only allowed
-to have private attributes of types ``label`` or ``label_list``. Attributes
-can be used to specify dependencies on tools or libraries that are needed
-for actions generated by aspects.
+``attrs`` defines a set of attributes for aspects. Aspects are allowed
+to have private attributes of types ``label`` or ``label_list``. Private label
+attributes can be used to specify dependencies on tools or libraries that are
+needed for actions generated by aspects. Aspects may also have normal attributes
+of type ``string``, called parameters, so long as ``values`` is specified. Any
+string attributes must match string attributes on the Skylark rule requesting
+the aspect, and they inherit their value from the rule. Aspects with parameters
+cannot be requested on the bazel command-line.
 
 ### Implementation functions