Update README.md

Author: compuphase

README.md

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 # Embedded Debugging with the Black Magic Probe
-<img src="https://www.compuphase.com/electronics/blackmagicprobe-book.jpg" alt="Book cover" width="400" align="right">
+<img src="https://github.com/compuphase/Black-Magic-Probe-Book/blob/master/doc/blackmagicprobe-book.jpg" alt="Book cover" width="400" align="right">
 This guide covers setting up and using the <a href="https://github.com/blackmagic-debug/blackmagic/">Black Magic Probe</a>. The Black Magic Probe is a low cost JTAG/SWD probe for ARM Cortex micro-controllers. A distinguishing feature of the Black Magic Probe is that it embeds a GDB server. As a result, the GNU Debugger can directly connect to the Black Magic Probe.
 
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