Fix readme consistency issues (#652)

* Correct notation for checked checkbox in markdown
* Cleanup image and link notation for consistency
* Syntax highlighting
* Update alt for images and fix incorrect link

Co-authored-by: あく <alleteam@gmail.com>

ReadMe.md

@@ -2,14 +2,14 @@
 
 [![Discord](https://img.shields.io/discord/740930220399525928.svg?label=&logo=discord&logoColor=ffffff&color=7389D8&labelColor=6A7EC2)](http://flipperzero.one/discord)
 
-<img src="https://habrastorage.org/webt/eo/m0/e4/eom0e4btudte7nrhnyic-laiog0.png" />
+![Show me the code](https://habrastorage.org/webt/eo/m0/e4/eom0e4btudte7nrhnyic-laiog0.png)
 
 Welcome to [Flipper Zero](https://flipperzero.one/)'s Firmware repo!
 Our goal is to create nice and clean code with good documentation, to make it a pleasure for everyone to work with.
 
 # Update firmware
 
-<a href="https://update.flipperzero.one/">Get Latest Firmware from Update Server</a>
+[Get Latest Firmware from Update Server](https://update.flipperzero.one/)
 
 
 Flipper Zero's firmware consists of three components:
@@ -51,7 +51,7 @@ One liner: `./flash_core1_main.sh`
  - Press and hold `← Left` + `↩ Back` for reset 
  - Release `← Left` and keep holding `↩ Back` until blue LED lights up
  - Release `↩ Back`
-<img src="https://habrastorage.org/webt/uu/c3/g2/uuc3g2n36f2sju19rskcvjzjf6w.png" />
+![Switch to DFU sequence](https://habrastorage.org/webt/uu/c3/g2/uuc3g2n36f2sju19rskcvjzjf6w.png)
 
 1. Run `dfu-util -D full.dfu -a 0`