README.md: update documentation of module versioning

Since x/ repos are now automatically periodically tagged, the previous
definition of the minor and patch versions of this module are now
obsolete. Delete that section of the README; regular semantic versioning
rules apply here.

Fixes golang/go#57089

Change-Id: I394ae4bb4eec1aa21c26b678b9ed1251b1eecf14
Reviewed-on: https://go-review.googlesource.com/c/text/+/455516
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Damien Neil <dneil@google.com>
Auto-Submit: Damien Neil <dneil@google.com>

README.md

@@ -4,19 +4,7 @@
 
 This repository holds supplementary Go libraries for text processing, many involving Unicode.
 
-## Semantic Versioning
-This repo uses Semantic versioning (http://semver.org/), so
-1. MAJOR version when you make incompatible API changes,
-1. MINOR version when you add functionality in a backwards-compatible manner,
-   and
-1. PATCH version when you make backwards-compatible bug fixes.
-
-Until version 1.0.0 of x/text is reached, the minor version is considered a
-major version. So going from 0.1.0 to 0.2.0 is considered to be a major version
-bump.
-
-A major new CLDR version is mapped to a minor version increase in x/text.
-Any other new CLDR version is mapped to a patch version increase in x/text.
+## CLDR Versioning
 
 It is important that the Unicode version used in `x/text` matches the one used
 by your Go compiler. The `x/text` repository supports multiple versions of