Standardise Flow's exe installer + readme update

[jjw24]

Standardise Flow's exe installer by removing the version at the end, this will make it easier to link to the latest download e.g. https://github.com/Flow-Launcher/Flow.Launcher/releases/latest/download/Flow-Launcher-Setup.exe

Tested:

1. changed the build version to 1.0.0 for testing
2. downloaded the artifact after build
3. Enabled portable mode
4. moved to different location
5. disabled portable mode
6. update to the latest via update command in query window
7. redid the steps 2-5 and updated flow via settings About tab
8. redid 2-7 for portable zip version

Updated readme to fix c# plugin dev doc and getting started section

[pc223]

Seems run normally on my machine, I can't test the update though, it's already 1.8.1 on my machine

[jjw24]

Seems run normally on my machine, I can't test the update though, it's already 1.8.1 on my machine

You can use this command in cmd prompt to build the artifacts locally:
Call powershell.exe -NoProfile -ExecutionPolicy Bypass -File <PATH-TO-FLOW-SOLUTION-FOLDER>\Scripts\post_build.ps1 Release <PATH-TO-FLOW-SOLUTION-FOLDER>

This will also build flow as 1.0.0, you can then upgrade