[docs] fix grammar mistake (#121695)

Fix a grammar mistake in Polly docs.

Co-authored-by: hstk30-hw <[email protected]>

Author: alyanser

polly/docs/UsingPollyWithClang.rst

@@ -101,7 +101,7 @@ polly, after SSA transformation, loop canonicalization, inlining and
 other passes.
 
 Thereafter, any Polly pass can be run over 'before-polly.ll' using the
-'opt' tool.  To found out which Polly passes are active in the standard
+'opt' tool.  To find out which Polly passes are active in the standard
 pipeline, see the output of
 
 .. code-block:: console