docs: source idf export.sh before running matter install.sh

This is the reason people are seeing lark issue. Is is fixed in CI but
on development host, if we follow the steps mentioned in the doc then it
installs lark in our native python environment. By sourcing idf's
export.sh it will install lark in idf's environment.

docs/en/developing.rst

@@ -54,6 +54,7 @@ For using VSCode for developement, please check `Developing in WSL <https://code
       git clone --recursive https://github.com/espressif/esp-idf.git
       cd esp-idf; git checkout v4.4.2; git submodule update --init --recursive;
       ./install.sh
+      . ./export.sh
       cd ..
 
 .. only:: esp32h2
@@ -63,6 +64,7 @@ For using VSCode for developement, please check `Developing in WSL <https://code
       git clone --recursive https://github.com/espressif/esp-idf.git
       cd esp-idf; git checkout 20949d444f; git submodule update --init --recursive;
       ./install.sh
+      . ./export.sh
       cd ..
 
 Cloning the esp-matter repository takes a while due to a lot of submodules in the upstream connectedhomeip,