runtime(vim): set 'path' to common Vim directories

[mateoxh]

ping @dkearns

[dkearns]

I don't understand the proposed value, wouldn't we want to use 'rtp'?

[mateoxh]

I find it useful when working on plugins or Vim's runtime files, for example it makes searching for files buried inside autoload/ easier.

I think 'rtp' adds too much noise and it's really not important for plugin development. Anyway, it's still better than the default value.