arch and manjaro install instructions are broken, outdated

[asafg]

The instructions here:

https://www.openastro.org/?Download

for Manjaro (arch) are broken on several places:

1. yaourt is discontinued

2. the link "https://aur.archlinux.org/packages/openastro/openastro.tar.gz" is 404, and i'm not sure how to find the correct link

3. on the "generic linux installation" section, package "librsvg2-bin" is not available in manjaro

4. python3-swisseph is not available for manjaro

5. I discovered that "yaourt" is replaced by "yay"; so I tried to install with "yay" (the heck) and running gave me this bug, which i'm going to report separately:

Traceback (most recent call last):
File "/usr/bin/openastro", line 6206, in <module>
  mainWindow()
File "/usr/bin/openastro", line 2898, in __init__
  self.tempfilename = openAstro.makeSVG()
File "/usr/bin/openastro", line 1339, in makeSVG
  module_data = ephemeris.ephData(self.year,self.month,self.day,self.hour,self.geolon, [...]
File "/usr/lib/python3.9/site-packages/openastromod/swiss.py", line 89, in __init__
  if ret_flag[0] >= deg_low:
TypeError: '>=' not supported between instances of 'tuple' and 'float'