docs(bridge-ui): add env values in the readme

[wolfderechter]

add default env values in the readme.
#8198
The values come from here. I used them locally and I was able to do transactions with my own local bridge.

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Name	Status	Preview	Updated
website	🔄 Building (Inspect)		Jan 6, 2023 at 11:29PM (UTC)

[codecov]

Codecov Report

Merging #11403 (d938d6c) into main (a8e82d5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main   #11403   +/-   ##
=======================================
  Coverage   65.99%   65.99%           
=======================================
  Files         108      108           
  Lines        2929     2929           
  Branches      355      355           
=======================================
  Hits         1933     1933           
  Misses        919      919           
  Partials       77       77           

Flag	Coverage Δ		*Carryforward flag
bridge-ui	95.05% <ø> (ø)
protocol	57.76% <ø> (ø)		Carriedforward from a8e82d5
relayer	69.10% <ø> (ø)		Carriedforward from a8e82d5
ui	100.00% <ø> (ø)		Carriedforward from a8e82d5

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[wolfderechter]

cc: @d1onys1us @shadab-taiko

[dantaik]

@shadab-taiko @d1onys1us Please also take a look at this.

[dionysuzx]

LGTM