doc: add tips file

doc/source/tips.rst

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+
+Tips & Tricks
+=============
+
+Image Ghosting
+--------------
+
+After multiple partial refreshes or drawing the same image multiple times,
+a ghosting effect may occur.
+That is, even after clearing the screen, the old image is still visible to a small degree.
+In order to avoid that and increase the lifetime of your display,
+you should first draw the inverse of an image before refreshing.
+
+If the old image is stored in `framebuf` and was drawn with `draw_mode` `BLACK_ON_WHITE`,
+the inverse image can be drawn with:
+::
+    
+    epd_draw_image(epd_full_screen(), framebuf, WHITE_ON_WHITE);
+
+
+Temperature Dependence
+----------------------
+
+The display refresh speed depends on the environmental temperature.
+Thus, if your room temperature is significantly different from ~22°C, grayscale
+accuracy might be affected.
+This can be mitigated by using a different timing curve, but this would require calibrating the display timings at that temperature.
+If you did this for some temperature other than room temperature, please submit a pull request!
+
+Deep Sleep Current
+------------------
+
+Board Revision V5 is optimized for running from a battery thanks to its low deep sleep current consumption. 
+In order to achieve the lowest possible deep sleep current, call
+::
+
+    epd_deinit()
+
+before going to deep sleep. This will de-initialize the I2S peripheral used to drive the diplay and bring the pins used by epdiy to a low-power state.
+You should be able to achieve a deep-sleep current of less than 13µA.
+If your deep-sleep current is much higher, please check your attached peripherals.
+With some modules, you have to isolate GPIO 12 before going to deep sleep:
+::
+
+    rtc_gpio_isolate(GPIO_NUM_12)
+
+
+