docs: Raspberry Pi OS - libcec build instructions (#47)

* readme: Fix typos/syntax of RasPi build instructions

* fix: Invalid syntax: `sudo cd`
* fix: typo `libp8 platform-dev` -> `p8-platform-dev`
* fix: Invalid syntax: `sudo rmdir -rf` -> `sudo rm -rf`

* oops

* readme: Raspberry Pi instructions -> gain superuser privs once

* Update README.md

README.md

@@ -30,27 +30,32 @@ If you are using Raspberry Pi OS and want to use the built-in HDMI port CEC, you
 
 Adapted from [libcec documentation](https://github.com/Pulse-Eight/libcec/blob/master/docs/README.raspberrypi.md):
 
-```
+```sh
+# Become superuser
+sudo su
+
 # Remove libcec (since we are going to build it ourselves)
 apt-get remove libcec6
 
 # Install libcec build dependencies, but not libcec itself
-sudo apt-get install libp8 platform-dev libp8-platform cmake libudev-dev libxrandr-dev python3-dev swig git
+apt-get install libp8-platform-dev libp8-platform2 cmake libudev-dev libxrandr-dev python3-dev swig git
 
 # Build libcec 6.0.2 with RPI CEC driver enabled
-sudo rmdir -rf /tmp/libcec-build-tmp
-sudo mkdir /tmp/libcec-build-tmp
-sudo cd /tmp/libcec-build-tmp
-sudo git clone --recursive https://github.com/Pulse-Eight/libcec.git
-sudo cd libcec
-sudo git checkout libcec-6.0.2
-sudo mkdir build
-sudo cd build
-sudo cmake -DRPI_INCLUDE_DIR=/opt/vc/include -DRPI_LIB_DIR=/opt/vc/lib ..
-sudo make -j4
-sudo make install
-sudo ldconfig
-
+rm -rf /tmp/libcec-build-tmp
+mkdir /tmp/libcec-build-tmp
+cd /tmp/libcec-build-tmp
+git clone --recursive https://github.com/Pulse-Eight/libcec.git
+cd libcec
+git checkout libcec-6.0.2
+mkdir build
+cd build
+cmake -DRPI_INCLUDE_DIR=/opt/vc/include -DRPI_LIB_DIR=/opt/vc/lib ..
+make -j4
+make install
+ldconfig
+
+# Leave superuser context
+exit
 ```
 
 ### Windows
@@ -95,4 +100,4 @@ See [CONTRIBUTING.md](CONTRIBUTING.md).
 
 ## Releasing
 
-```cargo release --no-publish --dev-version --execute``` and let the github CD pipeline do the rest.
+```cargo release --no-publish --dev-version --execute``` and let the github CD pipeline do the rest.