config: Added custom HSD launch command

- Added `HSD` and `HSD-command` keys to node.txt file
- Users can now set a custom HSD launch command by setting the `hsd-command` key in node.txt
- README.md updated with instructions on how to set a custom HSD launch command using `{default-dir}`, `{key}` and `{Bob}`
- Support section added to README.md

example-configs/node.txt

@@ -1,3 +1,5 @@
 IP: 127.0.0.1
 Network: 0
 Key: my-super-secret-api-key
+HSD: False
+HSD-command: {default-dir} --agent=FireWallet --index-tx --index-address --api-key {key} --prefix {Bob}