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: Ic79f28fcb8a68a1757f10bf2e3cd3656a11fec73
diff --git a/README.md b/README.md
index 1b9d67f..89aba20 100644
--- a/README.md
+++ b/README.md
@@ -2,12 +2,12 @@
 
 ## To Build
 
-```
 To build this package, do the following steps:
 
-    1. ./bootstrap.sh
-    2. ./configure ${CONFIGURE_FLAGS}
-    3. make
+```sh
+1. ./bootstrap.sh
+2. ./configure ${CONFIGURE_FLAGS}
+3. make
+```
 
 To clean the repository run `./bootstrap.sh clean`.
-```