doc: add default values in signature

README.md

@@ -19,7 +19,7 @@ Requires `bash`.
 Signature:
 
 ```shell
-wait_for_url url<string> [iterations<int> duration<int>]
+wait_for_url url<string> [iterations<int>=1 duration<int>=1]
 ```
 
 Usage:
@@ -46,7 +46,7 @@ Requires `bash`.
 Signature:
 
 ```shell
-wait_for_pid_exit pid<int> [iterations<int> duration<int>]
+wait_for_pid_exit pid<int> [iterations<int>=3 duration<int>=1]
 ```
 
 Usage:
@@ -66,12 +66,12 @@ wait_for_pid_exit 3618 5 3
 
 ## `error_and_exit $message`
 
-Prints an error message and then exits with exit code `1`.
+Prints an error message and then exits with exit code `1`. The message defaults to `error`
 
 Signature:
 
 ```shell
-error_and_exit [message<string>]
+error_and_exit [message<string>=error]
 ```
 
 Usage: