libseife [TASK][DOC]: specify tidal constituents

specify the tidal constituents used for tide removal in a source code
comment

src/libs/libseife/cseife_tides.c

@@ -52,6 +52,19 @@ void seife_tid(double* x, int n, double dt, int nstep)
 {
     /* Initialized data */
 
+/* tidal constituents used:
+ *
+ * f /cpd         f / deg/h   constituent
+ * ------         ---------   -----------
+ * 0.89293        13.39395	Q1
+ * 0.92954        13.9431	O1
+ * 1.00274        15.0411	K1
+ * 1.89567        28.43505	N2
+ * 1.93227        28.98405	M2
+ * 2              30          S2
+ * 2.898450424    43.47675636 M3
+*/
+
 #define C_MFREQ 7
 #define C_MDIM (C_MFREQ*2+1)
     static double omega[C_MFREQ] = { 2.898450424,

src/libs/libseife/subs/seife_tides.f

@@ -38,6 +38,8 @@ c  to the total length of the record.
       character par*35,msg*(*)
       dimension x(n),a(13,13),rs(13),c(13),d(13),e(13),f(13),
      & omega(6),omeg(6),cor(6)
+c
+c see comment in cseife_tides.c for a definition of tidal constituents
       data omega/1.93227d0,0.92954d0,2.00000d0,1.00274d0,1.89567d0,
      & 0.89293d0/
       data zero,one,two/0.d0,1.d0,2.d0/