Add a gdb cheat sheet

cheatsheets/gdb

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+# start the debugger
+gdb your-executable
+
+# set a breakpoint
+b some-method, break some-method
+
+# run the program
+r, run
+
+# when a breakpoint was reached:
+
+# run the current line, stepping over any invocations
+n, next
+# run the current line, stepping into any invocations
+s, step
+# print a stacktrace
+bt, backtrace
+# evaluate an expression and print the result
+p length=strlen(string)
+# list surrounding source code
+l, list
+# continue execution
+c, continue
+
+# exit gdb (after program terminated)
+q, quit