docs(floating-ip): explain when server_id is required (#978)

Related to #977

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Co-authored-by: Jonas L. <jooola@users.noreply.github.com>

Author: apricote

website/docs/r/floating_ip.html.md

@@ -29,8 +29,8 @@ resource "hcloud_floating_ip" "master" {
 
 - `type` - (Required, string) Type of the Floating IP. `ipv4` `ipv6`
 - `name` - (Optional, string) Name of the Floating IP.
-- `server_id` - (Optional, int) Server to assign the Floating IP to.
-- `home_location` - (Optional, string) Name of home location (routing is optimized for that location). Optional if server_id argument is passed.
+- `server_id` - (Optional, int) Server to assign the Floating IP to. Optional if `home_location` argument is passed.
+- `home_location` - (Optional, string) Name of home location (routing is optimized for that location). Optional if `server_id` argument is passed.
 - `description` - (Optional, string) Description of the Floating IP.
 - `labels` - (Optional, map) User-defined labels (key-value pairs) should be created with.
 - `delete_protection` - (Optional, bool) Enable or disable delete protection. See ["Delete Protection"](../index.html.markdown#delete-protection) in the Provider Docs for details.