README.md: Fix MD040 warnings

The following warnings are generated by using markdownlint analysis:
```
MD040/fenced-code-language Fenced code blocks should have a language specified [Context: "```"]
```
Refer to markdown-lint [1] to fix MD040
[1]: https://github.com/updownpress/markdown-lint/blob/master/rules/040-fenced-code-language.md

Change-Id: I91e8b62a4947109e28f2b5b5768f32bd52b1e21b
Signed-off-by: George Liu <liuxiwei@ieisystem.com>
diff --git a/README.md b/README.md
index bf91a92..07ed9b1 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@
 
 This project uses Meson (>=1.1.1). To build for native architecture, simply run:
 
-```
+```sh
 meson setup build
 ninji -C build
 ```
@@ -26,7 +26,7 @@
 that can be found in `build/`. With this, you can convert to and from CPER and
 CPER-JSON through the command line. An example usage scenario is below:
 
-```
+```sh
 cper-convert to-cper samples/cper-json-test-arm.json --out cper.dump
 cper-convert to-json cper.generated.dump
 ```
@@ -35,7 +35,7 @@
 This allows you to generate pseudo-random valid CPER records with sections of
 specified types for testing purposes. An example use of the program is below:
 
-```
+```sh
 cper-generate --out cper.generated.dump --sections generic ia32x64
 ```
 
@@ -46,7 +46,7 @@
 between an intermediate JSON format can be found generated at
 `lib/libcper-parse.a`. This contains the following useful library symbols:
 
-```
+```sh
 json_object* cper_to_ir(FILE* cper_file);
 void ir_to_cper(json_object* ir, FILE* out);
 ```