Ledger Wallet CLi guide

+ Based on [dEBRUYNE StackExchange Post](https://monero.stackexchange.com/questions/8503/how-do-i-generate-a-ledger-monero-wallet-with-the-cli-monero-wallet-cli)
+ De-personalized (s/"I"/"We"/g)
+ Download links moved to getmonero.org instead of GitHub
+ Typo Correction
  - Mac OS referring to GUI 0.12.1.0 instead of CLI 0.12.2.0
  - Monero v0.12.1.0 mentioned instead of v0.12.2.0
  - s/cavaet/caveat/g
+ Precision on installation section of Ledger Monero app guide for windows
+ Update the "need assistance" final note to link to the StackExchange answer.
+ Update to latest edit from @dEBRUYNE-1 on 2018/06/06
+ Corrections after review
+ consistency checks