[README] Installation howto is outdated and update howto doesn't exist

[yermulnik]

The problem

Ref: #469

• The «If you want to use this, please copy the script from here» in README leads to incorrect (outdated) version of GAS
• The Wiki: Setting up the script manually is outdated as is missing filters.gs
• No update guidance is provided. The process is intuitively clear (copy over files content from repo to GAS project), whilst might be non-obvious for beginners (and tripped me over by a missing file from the item above)

[jonas0b1011001]

Could you help us update/improve the wiki as you've just used it and had issues?

[yermulnik]

Could you help us update/improve the wiki as you've just used it and had issues?

#471

Patch to Wiki:
0001-docs-Add-filters.gs-to-Wiki.patch.txt