fixed URLs in documentation

[edwardhartnett]

Fixes NOAA-EMC/NCEPLIBS-grib_util#344
Fixes #314
Fixes #309

[edwardhartnett]

This is failing like this:

/usr/bin/gfortran -g -funroll-loops  -fallow-argument-mismatch -O3 CMakeFiles/tocgrib.dir/makwmo.F90.o CMakeFiles/tocgrib.dir/mkfldsep.F90.o CMakeFiles/tocgrib.dir/tocgrib.F90.o -o tocgrib  /home/runner/bacio/lib/libbacio.a /home/runner/w3emc/lib/libw3emc_4.a /home/runner/bacio/lib/libbacio.a
/usr/bin/ld: CMakeFiles/tocgrib.dir/tocgrib.F90.o: in function `MAIN__':
/home/runner/work/NCEPLIBS-g2/NCEPLIBS-g2/g2/utils/tocgrib.F90:73: undefined reference to `w3as00_'
collect2: error: ld returned 1 exit status
make[2]: *** [utils/CMakeFiles/tocgrib.dir/build.make:129: utils/tocgrib] Error 1
make[2]: Leaving directory '/home/runner/work/NCEPLIBS-g2/NCEPLIBS-g2/g2/build'
make[1]: *** [CMakeFiles/Makefile2:1536: utils/CMakeFiles/tocgrib.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....

But this PR contains only documentation changes...