selectrum: improve bindings

- add missing emacs bindings
- properly feature guard swiper related bindings
- for selectrum, unbind `SPC s B` and temporarily bind `SPC s s` to
  isearch to prevent don't get errors until we decide what to do there.
- update readme to reflect that

modules/completion/selectrum/README.org

@@ -105,17 +105,15 @@ users).
 https://assets.doomemacs.org/completion/selectrum/search-replace.png
 
 ** TODO In-buffer searching
-The =swiper= package provides an interactive buffer search powered by ivy. It
-can be invoked with:
+This module provides some in buffer searching bindings:
 
-+ =SPC s s= (~swiper-isearch~)
-+ =SPC s S= (~swiper-isearch-thing-at-point~)
++ =SPC s s= (~isearch~)
++ =SPC s S= (~+selectrum/search-symbol-at-point~ via ~consult-line~)
 + =SPC s b= (~consult-line~)
-+ ~:sw[iper] [QUERY]~
 
 https://assets.doomemacs.org/completion/selectrum/buffer-search.png
 
-A wgrep buffer can be opened from swiper with =C-c C-e=.
+A wgrep buffer can be opened from ~consult-line~ with =C-c C-e= (not yet).
 
 ** Selectrum integration for various completing commands
 *** General