README.md: fix a typo

Fix a hyperlink that was in incorrect format.

BUG=None
TEST=check the README.md in Chrome browser

Change-Id: I372a523adc0ee7465fd647fabf3316c863fe03e1
Reviewed-on: https://chromium-review.googlesource.com/1902992
Tested-by: Wei-Han Chen <stimim@chromium.org>
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Chun-Tsen Kuo <chuntsen@chromium.org>
diff --git a/README.md b/README.md
index 22c453a..a25989c 100644
--- a/README.md
+++ b/README.md
@@ -294,7 +294,7 @@
 If the Netboot firmware `image.net.bin` is available, flash the that to main
 (AP) SPI firmware and just boot. You will need to setup the network environment
 (details to be provided in future) so it can download a special kernel and then
-run same installer as [Boot from USB](#Boot-from-USB]. For more details, please
+run same installer as [Boot from USB](#Boot-from-USB). For more details, please
 refer to [Netboot Setup](./setup/NETBOOT.md).
 
 ### Pre-Installation (Copy Machine)