add managing changes markdown

pages/Managing changes.md

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+Managing changes
+----------------
+
+speedwm's Makefile has a nice feature which allows you to compile one header into the binary while keeping the original unmodified.
+
+If I want to make a change to, let's say `bar.h` in my personal build I just `cp bar.h bar.rl.h`, make changes to `bar.rl.h` and recompile. `bar.h` will be intact, but my changes from bar.rl.h will be applied in the compiled binary.
+
+This feature is currently available for:
+
+- bar.h
+- options.h
+- keybinds.h
+- mouse.h
+- status.h