BeagleV-Fire Documentation Update: Addition of Libero introduction demo and small fixes

In this PR, the following changes are introduced:

• Addition of a demo "Exploring Gateware Design with Libero" for users who want to get their hands into developing through the Microchip IDE in exploring-gateware-design-libero.rst.
• Fixing a broken link in customize-cape-gateware-verilog.rst and a couple of typos in flashing-board.rst.
• Added clock informations for users in index.rst
• Added information for building the project files for libero in gateware-tcl-scripts-structure.rst