iteflash.md: Update link to CrOS EC development doc
BRANCH=none
TEST=Used Gitiles to view and follow the updated link.
@@ -6,7 +6,7 @@ First written: 2019-04-02
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Last updated: 2019-04-03
-Familiarity with [Chromium OS](https://www.chromium.org/chromium-os) [Embedded Controller (EC) development](https://www.chromium.org/chromium-os/ec-development) is assumed.
+Familiarity with [Chromium OS](https://www.chromium.org/chromium-os) [Embedded Controller (EC) development](../README.md) is assumed.
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