Update readme to tell about feature freeze on 1.9

[theminer3746]

I have read many PRs updating/adding localization after #1851 was announced.
Those people definitely have good intention, but their time and effort ultimately didn't get to go in production.
So I created this PR to tell them to join in on Faker 2.0 design discussion instead.

[codecov-io]

Codecov Report

Merging #1875 into master will decrease coverage by 0.41%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #1875      +/-   ##
============================================
- Coverage     56.87%   56.46%   -0.42%     
  Complexity     2068     2068              
============================================
  Files           306      306              
  Lines          4851     4851              
============================================
- Hits           2759     2739      -20     
- Misses         2092     2112      +20

Impacted Files	Coverage Δ	Complexity Δ
src/Faker/Provider/hr_HR/Company.php	0% <0%> (-100%)	1% <0%> (ø)
src/Faker/Provider/en_IN/Person.php	0% <0%> (-100%)	1% <0%> (ø)
src/Faker/Provider/ko_KR/Company.php	50% <0%> (-50%)	2% <0%> (ø)
src/Faker/Provider/vi_VN/Person.php	20% <0%> (-40%)	5% <0%> (ø)
src/Faker/Provider/ro_MD/Address.php	65.21% <0%> (-34.79%)	10% <0%> (ø)
src/Faker/Provider/cs_CZ/Address.php	66.66% <0%> (-33.34%)	3% <0%> (ø)
src/Faker/Provider/en_AU/Address.php	75% <0%> (-25%)	4% <0%> (ø)
src/Faker/Provider/sv_SE/Address.php	75% <0%> (-25%)	4% <0%> (ø)
src/Faker/Provider/es_VE/Address.php	75% <0%> (-25%)	4% <0%> (ø)
src/Faker/Provider/it_IT/Address.php	75% <0%> (-25%)	4% <0%> (ø)
... and 36 more

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