Update README.md

http://cartodb.com/map 404 error.
Update README.md
Update README.md
Update README.md

changed POSTGIS_SQL_PATH='pg_config --sharedir'/contrib/postgis-2.0 to POSTGIS_SQL_PATH=`pg_config --sharedir`/contrib/postgis-2.0
Readme didn't say to connect to cartodb/base ppa
CDB-2757 Implemented sync now functionality along the way (@see ticket CDB-1100)
CDB-2757 Added superadmin endpoint for listing all users synchronizations
CDB-2757 Sync filter
Merge branch 'master' into CDB-2757
Removes unused code. Fixes failing spec
Fixes spec
using https urls for cartodb basemaps CDB-2711
Fixes spec
Missing attributes in testing app_config geocoder
Merge branch 'master' into CDB-2773
Merge pull request #393 from CartoDB/CDB-2773

Fixes some tests
Merge pull request #353 from varunbhuvanendran/master

edit some links
Merge pull request #367 from varunbhuvanendran/patch-1

Update README.md
Merge remote-tracking branch 'origin/master' into CDB-2711
Merge pull request #394 from CartoDB/CDB-2711

using https urls for cartodb basemaps CDB-2711