Update README.txt

Edits for clarity and grammar.
Merge pull request #111 from mc130c-att-com/patch-1

Merge README.txt
Editorial review
Merge pull request #112 from mc130c-att-com/patch-2

Editorial review
Editorial Review, fixed graphic paths
One-letter editorial change
Editorial changes for style and grammar
Editorial changes for grammar and style
Put back correct relative link
Update readme.md
Minor editorial changes
Minor editorial changes.
Spell out IAM in the interface doc of the logout function
Merge branch 'v4.2-doc' into develop