Update git submodules

* Update docs/submodules/clamp.git from branch 'master'
  to a21d8b67351580c90cd848d0742e395155ed6e20
  - Enhance readthedoc contents
    
    add a bit more details information in readthedoc
    
    Issue-ID: CLAMP-257
    
    Change-Id: I79a482b17a4f1d0fac2d215a389784a70a73f8bc
    Signed-off-by: osgn422w <gervais-martial.ngueko@intl.att.com>
    
1 file changed