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

Signed-off-by: George Liu <liuxiwei@ieisystem.com>
Change-Id: I699248975a3ebf01436031d0a865f2b70a575720
diff --git a/README.md b/README.md
index f76e7a8..015dc5a 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@
 
 For a standard release build, you want something like:
 
-```
+```sh
 meson setup -Dexamples=false -Dtests=disabled builddir
 ninja -C builddir
 ninja -C builddir install
@@ -15,7 +15,7 @@
 
 For a test / debug build, a typical configuration is
 
-```
+```sh
 meson setup -Dtests=enabled builddir
 meson test -C builddir
 ```