Don't tell users to use a bad number of threads (#243)

The readme tells people to use the command line option "-t 8", causing 8
threads to be started. On systems with fewer than 8 cores, this causes a
significant slowdown. Remove the option from the example command lines
and use /proc/cpuinfo on Linux to determine a sensible default.

ggml.c

@@ -9318,10 +9318,6 @@ static thread_ret_t ggml_graph_compute_thread(void * data) {
 }
 
 void ggml_graph_compute(struct ggml_context * ctx, struct ggml_cgraph * cgraph) {
-    if (cgraph->n_threads <= 0) {
-        cgraph->n_threads = 8;
-    }
-
     const int n_threads = cgraph->n_threads;
 
     struct ggml_compute_state_shared state_shared = {