Include plaintext instance list in repo [skip ci]

Including a list of instances that are easily machine-readable allows
services such as Farside (https://github.com/benbusby/farside) to read
these and have an up to date list of valid instances.

misc/instances.txt

@@ -0,0 +1,8 @@
+https://s.alefvanoon.xyz
+https://search.albony.xyz
+https://search.exonip.de
+https://search.garudalinux.org
+https://search.sethforprivacy.com
+https://whoogle.fossho.st
+https://whooglesearch.net
+https://www.whooglesearch.ml