Change gitignore files to relative paths and fix READMEs

Created by: senk

• Fix READMEs introducing wrong gitignore entries
• Change .gitignore files to include correct relative paths

Using absolute paths for these was not a mistake. In big projects, it could happen for some third party lib folder to be used deeper than the root level. Using relative paths would break this by ignoring every lib folder, which is not what we want (unlike node_modules, which we always want to ignore).

Created by: senk

You're absolutely right. Thanks for pointing that out :)

closed