Add example of detaching peripheral clock and varying system clock

clocks/detached_clk_peri/CMakeLists.txt

@@ -0,0 +1,12 @@
+add_executable(clocks_detached_clk_peri
+        detached_clk_peri.c
+        )
+
+# Pull in our pico_stdlib which pulls in commonly used features
+target_link_libraries(clocks_detached_clk_peri pico_stdlib)
+
+# create map/bin/hex file etc.
+pico_add_extra_outputs(clocks_detached_clk_peri)
+
+# add url via pico_set_program_url
+example_auto_set_url(clocks_detached_clk_peri)