Add missing dependency.

Merges https://github.com/espressif/esp-idf/pull/2781

docs/en/api-guides/jtag-debugging/building-openocd-macos.rst

@@ -22,7 +22,7 @@ Install Dependencies
 
 Install packages that are required to compile OpenOCD using Homebrew::
 
-	brew install automake libtool libusb wget gcc@4.9
+	brew install automake libtool libusb wget gcc@4.9 pkg-config
 
 Build OpenOCD
 =============
@@ -51,4 +51,4 @@ Next Steps
 
 To carry on with debugging environment setup, proceed to section :ref:`jtag-debugging-configuring-esp32-target`.
 
-    
+