reorg the documentation section order.
reorg the documentation section order.

Promote the 'CONFIGURATION' section to the front because I expect people to read
individual command documentation via running `perlbrew help <command>`, which makes
them less important when reading the whole document.

ptolemarch/App-perlbrew,josl/App-perlbrew,rafl/App-perlbrew,dagolden/App-perlbrew,Asuza/App-perlbrew,josl/App-perlbrew,ptolemarch/App-perlbrew,Asuza/App-perlbrew,josl/App-perlbrew,Asuza/App-perlbrew,rafl/App-perlbrew,calid/App-perlbrew,ptolemarch/App-perlbrew,dagolden/App-perlbrew,calid/App-perlbrew,rafl/App-perlbrew