Added to README, refactor, more flexibility

[swiftlee]

Changes:

README.md Minor changes to the README to give better instruction on how to run the program.

Program.cs

• Refactored usages of "var" and boolean expressions to be more consistent and readable.
• Allow base path to include backslashes.
• Allow other URLs besides the /Books endpoint.
• Added console prompt for entering your own URLs.

.gitignore Added support for JetBrains Rider so that .idea/ directory is ignored.