[chore][receiver/filelog]: add hyperlink to operator docs (open-telem…

…etry#26260)

**Description:** 
I'm adding this for readability and convenience - it seems reasonable
and intuitive to be able to jump to operator docs from that place.

receiver/filelogreceiver/README.md

@@ -60,7 +60,7 @@ Note that _by default_, no logs will be read from a file that is not actively be
 
 ### Operators
 
-Each operator performs a simple responsibility, such as parsing a timestamp or JSON. Chain together operators to process logs into a desired format.
+Each [operator](../../pkg/stanza/docs/operators/README.md#what-is-an-operator) performs a simple responsibility, such as parsing a timestamp or JSON. Chain together operators to process logs into a desired format.
 
 - Every operator has a `type`.
 - Every operator can be given a unique `id`. If you use the same type of operator more than once in a pipeline, you must specify an `id`. Otherwise, the `id` defaults to the value of `type`.