Although the hyphen is optional, one can easily argue that 'How-tos' is preferable to 'How tos'. A non-native speaker may not understand that the expression refers to an object (a guide), so it may look up the definition of 'tos'. Using 'How-tos' helps in this sense, as it indicates that it is a single expression.
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Sunburst
The inner-most circle is the entire project, moving away from the center are folders then, finally, a single file.
The size and color of each slice is representing the number of statements and the coverage, respectively.
Icicle
The top section represents the entire project. Proceeding with folders and finally individual files.
The size and color of each slice is representing the number of statements and the coverage, respectively.