Add link to detailed Net::HTTP documentation in README Usage section

[tkf0029]

Problem

When looking at the README on GitHub, it's unclear where to find more detailed information.

The README for the Net::HTTP gem includes the following sections:

• Overview
• Installation
• Usage
  • GET
  • GET by URI
  • GET with Dynamic Parameters
  • POST
  • POST with Multiple Values
• Development
• Contributing

The file net-http/doc/net-http/examples.rdoc also contains some simple usage examples.

However, it is not clear where to look for following information:

• Details of the get or post_form methods used in the sample code:
  • Supported argument types
  • Return values
• Other ways to implement GET or POST requests
• Links to documentation covering the above

---

Objective

To allow users of the net-http gem to easily find detailed information and sample code for implementing basic HTTP requests using net-http.

---

Proposal

Add a link at the bottom of the README's Usage section pointing to documentation with more detailed information.

---

The link is added only, without duplicating examples from rdoc, to avoid divergence between the README and official documentation.