Revert errors changing master to main in docs

docs/px4_build.md

@@ -14,7 +14,7 @@ Now to build it you will need the right tools.
 
 ## PX4 Build tools
 
-The full instructions are available on the [dev.px4.io](https://docs.px4.io/main/en/dev_setup/building_px4.html) website,
+The full instructions are available on the [dev.px4.io](https://docs.px4.io/master/en/dev_setup/building_px4.html) website,
 but we've copied the relevant subset of those instructions here for your convenience.
 
 (Note that [BashOnWindows](https://msdn.microsoft.com/en-us/commandline/wsl/install_guide)) can be used to build

docs/px4_lockstep.md

@@ -1,7 +1,7 @@
 # LockStep
 
 The latest version of PX4 supports a new [lockstep
-feature](https://docs.px4.io/main/en/simulation/#lockstep-simulation) when communicating with the
+feature](https://docs.px4.io/master/en/simulation/#lockstep-simulation) when communicating with the
 simulator over TCP.  Lockstep is an important feature because it synchronizes PX4 and the simulator
 so they essentially use the same clock time.  This makes PX4 behave normally even during unusually
 long delays in Simulator performance.
@@ -42,7 +42,7 @@ in the simulated flight if you look at the updates on screen in realtime.
 If you are running PX4 in cygwin, there is an [open issue with 
 lockstep](https://github.com/microsoft/AirSim/issues/3415). PX4 is configured to use lockstep by 
 default. To disable this feature, first [disable it in 
-PX4](https://docs.px4.io/main/en/simulation/#disable-lockstep-simulation):
+PX4](https://docs.px4.io/master/en/simulation/#disable-lockstep-simulation):
 
 1. Navigate to `boards/px4/sitl/` in your local PX4 repository
 1. Edit `default.cmake` and find the following line:

docs/px4_setup.md

@@ -64,7 +64,7 @@ are also enabling `LockStep`, see [PX4 LockStep](px4_lockstep.md) for more infor
 `Barometer` setting keeps PX4 happy because the default AirSim barometer has a bit too much noise
 generation.  This setting clamps that down a bit which allows PX4 to achieve GPS lock more quickly.
 
-After above setup you should be able to use a remote control (RC) to fly with AirSim. You can usually arm the vehicle by lowering and bringing two sticks of RC together down and in-wards. You don't need QGroundControl after the initial setup. Typically the Stabilized (instead of Manual) mode gives better experience for beginners.  See [PX4 Basic Flying Guide](https://docs.px4.io/main/en/flying/basic_flying.html).
+After above setup you should be able to use a remote control (RC) to fly with AirSim. You can usually arm the vehicle by lowering and bringing two sticks of RC together down and in-wards. You don't need QGroundControl after the initial setup. Typically the Stabilized (instead of Manual) mode gives better experience for beginners.  See [PX4 Basic Flying Guide](https://docs.px4.io/master/en/flying/basic_flying.html).
 
 You can also control the drone from [Python APIs](apis.md).
 

docs/px4_sitl.md

@@ -2,7 +2,7 @@
 
 The [PX4](http://dev.px4.io) software provides a "software-in-loop" simulation (SITL) version of
 their stack that runs in Linux. If you are on Windows then you can use the [Cygwin
-Toolchain](https://dev.px4.io/main/en/setup/dev_env_windows_cygwin.html) or you can use the
+Toolchain](https://dev.px4.io/master/en/setup/dev_env_windows_cygwin.html) or you can use the
 [Windows subsystem for Linux](https://docs.microsoft.com/en-us/windows/wsl/install-win10) and follow
 the PX4 Linux toolchain setup.
 
@@ -12,7 +12,7 @@ instructions](px4_sitl_wsl2.md).
 **Note** that every time you stop the unreal app you have to restart the `px4` app.
 
 1. From your bash terminal follow [these steps for
-   Linux](https://docs.px4.io/main/en/dev_setup/dev_env_linux.html) and follow **all** the
+   Linux](https://docs.px4.io/master/en/dev_setup/dev_env_linux.html) and follow **all** the
    instructions under `NuttX based hardware` to install prerequisites. We've also included our own
    copy of the [PX4 build instructions](px4_build.md) which is a bit more concise about what we need
    exactly.