Reformat the codeblocks in README.md

1. Remove the extra indent
2. Add `sh` language

README.md

@@ -30,22 +30,22 @@ This program is written in highly portable ANSI C. The only external dependencie
 
 On Debian/Ubuntu, you can satisfy these requirements by running
 
-```
-    apt install libssl-dev libcurl4-openssl-dev
+```sh
+apt install libssl-dev libcurl4-openssl-dev
 ```
 
 On OpenBSD you just need to install `curl`:
 
-```
-    pkg_add curl
+```sh
+pkg_add curl
 ```
 
 Run `make` and then `make install` as root.
 
 From version 2.27, `snac` includes support for the Mastodon API; if you are not interested on it, you can compile it out by running
 
-```
-    make CFLAGS=-DNO_MASTODON_API
+```sh
+make CFLAGS=-DNO_MASTODON_API
 ```
 
 See the administrator manual on how to proceed from here.
@@ -54,8 +54,8 @@ See the administrator manual on how to proceed from here.
 
 A `docker-compose` file is provided for development and testing. To start snac with an nginx HTTPS frontend, run:
 
-```
-    docker-compose build && docker-compose up
+```sh
+docker-compose build && docker-compose up
 ```
 
 This will: