Add placeholder Subversion cheat sheet
Add initial headings, topics
Add first draft command table coparison
Continued draft on migration approaches
Add SVN migration drafts
Fix typos, grammar
Revise intro tagline
Add vocabulary table col header clarification
Attempt first-pass vocabulary table descriptions
Tune Git SVN support section title
cleared up some command usage for remote / local

clone is used only once (dont want to confuse people about it being used in place of pull)

push is used to update github from local

use "GitHub" wording in place of remote or central after the firs ttime
Revise command vocabulary descriptions
Minor updates to Subversion cheat sheet
Tune wording, grammar, descriptions
Add detail about standard layout
Merge pull request #248 from github/cheatsheet-subversion-migration

Subversion migration cheat sheet (first edition)