Update readme with the new link to docs and branching

[denis-anisimov]

Part of fix for vaadin-button-flow/issues/83

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This change is 

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[ZheSun88]

sign the CLA

Reviewed 1 of 1 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @denis-anisimov)

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README.md, line 7 at r1 (raw file):

- `1.0` branch is Vaadin 10 LTS (Flow/Flow-component version 1.0)

1.0 branch should be Vaadin 10 compatible, but this component should not be LTS
same as grid 1.1 branch

[denis-anisimov]

Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @ZheSun88)

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README.md, line 7 at r1 (raw file):

Previously, ZheSun88 (Sun Zhe) wrote…

- `1.0` branch is Vaadin 10 LTS (Flow/Flow-component version 1.0)

1.0 branch should be Vaadin 10 compatible, but this component should not be LTS
same as grid 1.1 branch

Done.

[ZheSun88]

Reviewed 1 of 1 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved

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README.md, line 7 at r1 (raw file):

Previously, denis-anisimov (Denis) wrote…

Done.

mentioning (Flow version 1.0, but no LTS support)

[ZheSun88]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @denis-anisimov)

[ZheSun88]

Reviewed 1 of 1 files at r3.
Reviewable status: complete! all files reviewed, all discussions resolved