[Comgr][NFC] Document static libs option in README

Change-Id: I4a3213ba11fedde300f323d834eb17ad282841ef

Author: lamb-j

amd/comgr/README.md

@@ -77,6 +77,9 @@ Optionally,
 may be enabled during development via `-DADDRESS_SANITIZER=On` during the Comgr
 `cmake` step.
 
+Comgr can be built as a static library by passing
+`-DCOMGR_BUILD_SHARED_LIBS=OFF` during the Comgr `cmake` step.
+
 Depending on the Code Object Manager
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