M73 is missing C parameter

[galagithub]

I noticed in Marlin 2.1.2.4 that M73 also has a C parameter but the documentation only depicts the R and P parameters.

[ellensp]

Yip needs updated

From the code

M73: Set percentage complete (for display on LCD)

Example:

M73 P25.63 ; Set progress to 25.63%
 M73 R456   ; Set remaining time to 456 minutes
 M73 C12    ; Set next interaction countdown to 12 minutes
 M73        ; Report current values