Fix installation documentation.
Fix installation documentation.

- Add --ignore-scripts so that dev dependencies do not need to be installed.
- Install as ohm/. to avoid conflict with npmjs.org/package/ohm
coopsource/ohm,anfedorov/ohm,coopsource/ohm,DanielTomlinson/ohm,DanielTomlinson/ohm,coopsource/ohm,harc/ohm,anfedorov/ohm,harc/ohm,anfedorov/ohm,cdglabs/ohm,cdglabs/ohm,cdglabs/ohm,DanielTomlinson/ohm,harc/ohm