helper-function: fix formatting of bpf_probe_read_user_str.md

Fix formatting of the code block and some inline codes.

docs/linux/helper-function/bpf_probe_read_user_str.md

@@ -18,19 +18,21 @@ Copy a NUL terminated string from an unsafe user address _unsafe_ptr_ to _dst_.
 
 On success, returns the number of bytes that were written, including the terminal NUL. This makes this helper useful in tracing programs for reading strings, and more importantly to get its length at runtime. See the following snippet:
 
+```c
+SEC("kprobe/sys_open")
+void bpf_sys_open(struct pt_regs ctx) {
+    char buf[PATHLEN]; // PATHLEN is defined to 256
+    int res = bpf_probe_read_user_str(buf, sizeof(buf), ctx->di);
+    // Consume buf, for example push it to
+    // userspace via bpf_perf_event_output(); we
+    // can use res (the string length) as event
+    // size, after checking its boundaries.
+}
 ```
-SEC("kprobe/sys_open") void bpf_sys_open(struct pt_regs _ctx) {         char buf[PATHLEN]; // PATHLEN is defined to 256         int res = bpf_probe_read_user_str(buf, sizeof(buf),
-```
-
-                                          ctx->di);
-
-        // Consume buf, for example push it to // userspace via bpf_perf_event_output(); we // can use res (the string length) as event // size, after checking its boundaries.
-
-    }
 
 In comparison, using **bpf_probe_read_user**() helper here instead to read the string would require to estimate the length at compile time, and would often result in copying more memory than necessary.
 
-Another useful use case is when parsing individual process arguments or individual environment variables navigating _current_**->mm->arg_start** and _current_\ **->mm->env_start**: using this helper and the return value, one can quickly iterate at the right offset of the memory area.
+Another useful use case is when parsing individual process arguments or individual environment variables navigating **current->mm->arg_start** and **current->mm->env_start**: using this helper and the return value, one can quickly iterate at the right offset of the memory area.
 
 ### Returns