inga_tool: Mention the changed build dependencies
inga_tool: Describe the command line flags better

- Mention -s for reading out the EEPROM values
- -s for choosing a device based on the serial ID was changed
  to -u (to remove the clash with the -s from above)
Merge pull request #2 from DrMcCoy/inga_tool_readme

Update the README for inga_tool