Invoke linux prepare script the same way.

Telegram/build/prepare/linux.sh

@@ -6,5 +6,6 @@ popd > /dev/null
 
 
 cd $FullScriptPath/../docker/centos_env
+poetry install
 poetry run gen_dockerfile | DOCKER_BUILDKIT=1 docker build -t tdesktop:centos_env -
 cd $FullExecPath

docs/building-linux.md

@@ -1,23 +1,23 @@
 ## Build instructions for Linux using Docker
 
+### Prepare folder
+
+Choose a folder for the future build, for example **/home/user/TBuild**. It will be named ***BuildPath*** in the rest of this document. All commands will be launched from Terminal.
+
 ### Obtain your API credentials
 
 You will require **api_id** and **api_hash** to access the Telegram API servers. To learn how to obtain them [click here][api_credentials].
 
-### Clone source code
+### Clone source code and prepare libraries
+
+Install [poetry](https://python-poetry.org), go to ***BuildPath*** and run
 
     git clone --recursive https://github.com/telegramdesktop/tdesktop.git
-
-### Prepare libraries
-
-Install [poetry](https://python-poetry.org), go to the `tdesktop/Telegram/build/docker/centos_env` directory and run
-
-    poetry install
-    poetry run gen_dockerfile | DOCKER_BUILDKIT=1 docker build -t tdesktop:centos_env -
+    ./tdesktop/Telegram/build/prepare/linux.sh
 
 ### Building the project
 
-Go up to the `tdesktop` directory and run (using [your **api_id** and **api_hash**](#obtain-your-api-credentials))
+Go to ***BuildPath*/tdesktop** and run (using [your **api_id** and **api_hash**](#obtain-your-api-credentials))
 
     docker run --rm -it \
         -v $PWD:/usr/src/tdesktop \