Fix code block formatting in README.md (#195)

Signed-off-by: 林博仁(Buo-ren Lin) <[email protected]>

Author: brlin-tw

README.md

@@ -72,14 +72,14 @@ $ make
 * If system libcurl supports it by default nothing else has to be done
 
 * If a custom build of libcurl supports HTTP/3 which is installed in a different location, that can be set when running cmake:
-```
-$ cmake -D CUSTOM_LIBCURL_INSTALL_PATH=/absolute/path/to/custom/libcurl/install .
-```
+  ```
+  $ cmake -D CUSTOM_LIBCURL_INSTALL_PATH=/absolute/path/to/custom/libcurl/install .
+  ```
 
 * Just to test HTTP/3 support for development purpose, simply run the following command and wait for a long time:
-```
-$ ./development_build_with_http3.sh
-```
+  ```
+  $ ./development_build_with_http3.sh
+  ```
 
 ## INSTALL