update and cleaning of README files

update and cleaning of README files so we don't replicate what is already available somewhere else...

file	action
./cfgs/SHARED/README.rst	remove, duplicate of user guide
./cfgs/SHARED/README.namelists	remove, duplicate of user guide
./cfgs/README.rst	remove, duplicate of user guide
./cfgs/ORCA2_ICE_PISCES/IDL_scripts/README	keep , going to be updated to Py
./cfgs/GYRE_BFM/README.md	keep for compliance with ext code
./ext/FCM/README	keep for compliance with ext code
./ext/PPR/README.md	keep for compliance with ext code
./README.rst	update
./sette/README.rst	remove, obsolete
./src/TOP/README.rst	remove, duplicate of user guide
./src/NST/README.rst	remove, duplicate of user guide
./src/SAS/README.rst	remove, is a link to doc page
./src/README.rst	remove, useless
./src/OCE/USR/README.rst	remove, is a link to doc page
./src/OCE/ASM/README.rst	remove, is a link to doc page
./src/OCE/SBC/README.rst	remove, is a link to doc page
./src/OCE/OBS/README.rst	remove, is a link to doc page
./src/OCE/CRS/README.rst	remove, is a link to doc page
./tools/SIREN/README	keep , linked to user guide
./tools/SIREN/templates/README	keep , linked to user guide
./tools/WEIGHTS/README	keep , linked to user guide
./tools/WEIGHTS/SCRIP1.4/grids/README	keep , linked to user guide
./tools/OBSTOOLS/dataplot/README	keep , linked to user guide
./tools/DMP_TOOLS/README	keep , linked to user guide
./tools/NESTING/README	keep , linked to user guide
./tools/DOMAINcfg/README.rst	keep , linked to user guide
./tools/REBUILD_NEMO/README.rst	keep , linked to user guide
./tools/ABL_TOOLS/README.rst	keep , linked to user guide
./tools/README.rst	remove, duplicate of user guide
./tests/README.rst	need to be checked
./tests/ISOMIP+/EXPREF/README
./tests/ICE_AGRIF/EXPREF/README
./tests/ICB/README
./tests/ICE_ADV2D/EXPREF/README
./tests/ICE_RHEO/EXPREF/README
./tests/ADIAB_WAVE/README.md
./tests/CPL_OASIS/README.md
./tests/STATION_ASF/README.md
./tests/WAD/EXPREF/README.py