fix doc and sample apps links
fix doc and sample apps links

- link to LICENSE, too
- minor textual fixes
vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa,vespa-engine/vespa