Update README.md 'C wrapper' section (#630)

Fixed missing string length argument in C wrapper example functions. Copied from singleheader/demo.c

README.md

@@ -231,26 +231,29 @@ See the file `include/ada_c.h` for our C interface. We expect ASCII or UTF-8 str
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdbool.h>
+#include <string.h>
 
 static void ada_print(ada_string string) {
   printf("%.*s\n", (int)string.length, string.data);
 }
 
 int main(int c, char *arg[] ) {
-  ada_url url = ada_parse("https://username:[email protected]:8080/"
-      "pathname?query=true#hash-exists");
+  const char* input =
+      "https://username:[email protected]:8080/"
+      "pathname?query=true#hash-exists";
+  ada_url url = ada_parse(input, strlen(input));
   if(!ada_is_valid(url)) { puts("failure"); return EXIT_FAILURE; }
   ada_print(ada_get_href(url)); // prints https://username:password@host:8080/pathname?query=true#hash-exists
   ada_print(ada_get_protocol(url)); // prints https:
   ada_print(ada_get_username(url)); // prints username
-  ada_set_href(url, "https://www.yagiz.co");
+  ada_set_href(url, "https://www.yagiz.co", strlen("https://www.yagiz.co"));  
   if(!ada_is_valid(url)) { puts("failure"); return EXIT_FAILURE; }
-  ada_set_hash(url, "new-hash");
-  ada_set_hostname(url, "new-host");
-  ada_set_host(url, "changed-host:9090");
-  ada_set_pathname(url, "new-pathname");
-  ada_set_search(url, "new-search");
-  ada_set_protocol(url, "wss");
+  ada_set_hash(url, "new-hash", strlen("new-hash"));
+  ada_set_hostname(url, "new-host", strlen("new-host"));
+  ada_set_host(url, "changed-host:9090", strlen("changed-host:9090"));
+  ada_set_pathname(url, "new-pathname", strlen("new-pathname"));
+  ada_set_search(url, "new-search", strlen("new-search"));
+  ada_set_protocol(url, "wss", 3);  
   ada_print(ada_get_href(url)); // will print wss://changed-host:9090/new-pathname?new-search#new-hash
 
   // Manipulating search params