README.md: improvements and fixes.

Bugfixes:

• code markup
• repokey URL

Improvements:

• replace http to https
• Ubuntu repo added

README.md

@@ -3,31 +3,40 @@ Cellframe Blockchain node
 
 [Cellframe Wiki](https://wiki.cellframe.net)
 
-## Build
-
-The project uses CMake. To generate a Makefile run in the project root directory `git submodule init && git submodule update --remote && cmake -S . -B build && cd ./build && make`.
-Or if you don't clone the project yet, run `git clone --recursive <repo>` to clone it with all submodules. Then build the project as a regular CMake project with command `cmake -S . -B build && cd ./build && make`.
-
-##How to install:
-
-### Debian and Ubuntu
-
-Create file /etc/apt/sources.list.d/demlabs.list with one line below:
-
-deb http://debian.pub.demlabs.net/ stretch main non-free
-
-Then download public signature and install it:
-
-wget https://debian.pub.demlabs.net/demlabskey.asc
-apt-key add demlabskey.asc
-
-Then update your apt cache and install the package:
-
-apt-get update
-apt-get install cellframe-node
-
-
-### Prerequsites
+## Build:
+
+* The project uses CMake. To generate a Makefile run in the project root directory:
+  ```
+  git submodule init
+  git submodule update --remote
+  cmake -S . -B build && make -C build
+  ```
+* Or if you don't clone the project yet:
+  ```
+  git clone --recursive <repo>
+  cmake -S . -B build && make -C build
+  ```
+
+## How to install:
+
+### Debian and Ubuntu:
+
+* Create file /etc/apt/sources.list.d/demlabs.list with one line below:
+  ```
+  deb http://debian.pub.demlabs.net/ stretch main non-free
+  ```
+* Then download public signature and install it:
+  ```
+  wget https://debian.pub.demlabs.net/demlabskey.asc
+  apt-key add demlabskey.asc
+  ```
+* Then update your apt cache and install the package:
+  ```
+  apt-get update
+  apt-get install cellframe-node
+  ```
+
+### Prerequsites:
 
 To successfully complete of the build, you must have following prerequisites preinstalled (packages are named as in Debian GNU/Linux 10 "buster", please found the corresponding packages for your distribution):