[WP][DOC] (libstfinv): finish summary of usage information

src/libs/libstfinv/usage/stfinvany_summary_usage.txt

 # this is <stfinvany_summary_usage.txt>
 # ----------------------------------------------------------------------------
 #
-Available procedures
-====================
-Summary
--------
-NO YET IMPLEMENTED!
+Syntax for parameter strings
+----------------------------
+Procedures can be selected by passing the procedures ID together with options
+an parameters controlling the algorithm used for the procedure.
+
+Syntax of parameter string:
+  ID:option:option=value:option=value
 # ----- END OF stfinvany_summary_usage.txt ----- 

src/libs/libstfinv/usage/stfinvfdleastsquares_summary_usage.txt

 # this is <stfinvfdleastsquares_summary_usage.txt>
 # ----------------------------------------------------------------------------
 #
-Fourier domain least squares procedure
-======================================
-Summary
--------
-NO YET IMPLEMENTED!
+Procedure: Least squares in the frequency domain
+------------------------------------------------
+Find optimal correction filter by waterlevel-deconvolution in the Fourier
+domain (i.e. least squares with regularization).
+
+Options and parameters:
+  waterlevel=l  waterlevel to be applied for regularization.
 # ----- END OF stfinvfdleastsquares_summary_usage.txt ----- 

src/libs/libstfinv/usage/stfinvidentity_summary_usage.txt

 # this is <stfinvidentity_summary_usage.txt>
 # ----------------------------------------------------------------------------
 #
-Scaling procedure
-=================
-Summary
--------
-NO YET IMPLEMENTED!
+Procedure: Scale with amplitude factor
+--------------------------------------
+Scaling signals by a scalar factor (i.e. keep signal shape).
+
+Options and parameters:
+  scaleenergy   if flag is set: scale energy
 # ----- END OF stfinvidentity_summary_usage.txt -----