docs: Match Single Blank Line Above and Below A Title

Signed-off-by: Yifei Ding <yifeiding@protonmail.com>

docs/TSL1401CL_Filament_Width_Sensor.md

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 This document describes Filament Width Sensor host module. Hardware used for developing this host module is based on TSL1401CL linear sensor array but it can work with any sensor array that has analog output. You can find designs at [thingiverse.com](https://www.thingiverse.com/search?q=filament%20width%20sensor)
 
 ## How does it work?
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 Sensor generates analog output based on calculated filament width. Output voltage always equals to detected filament width (Ex. 1.65v, 1.70v, 3.0v). Host module monitors voltage changes and adjusts extrusion multiplier.
 
 ## Configuration
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     [tsl1401cl_filament_width_sensor]
     pin: analog5
     # Analog input pin for sensor output on Ramps board
@@ -27,6 +29,7 @@ Sensor generates analog output based on calculated filament width. Output voltag
 Sensor readings done with 10 mm intervals by default. If necessary you are free to change this setting by editing ***MEASUREMENT_INTERVAL_MM*** parameter in **filament_width_sensor.py** file.
 
 ## Commands
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 **QUERY_FILAMENT_WIDTH** - Return the current measured filament width as result
 **RESET_FILAMENT_WIDTH_SENSOR** – Clear all sensor readings. Can be used after filament change.
 **DISABLE_FILAMENT_WIDTH_SENSOR** – Turn off the filament width sensor and stop using it to do flow control