[gcc(refs/vendors/microsoft/heads/main)] Update readme to refer to repo as mirror (#51)

[gcc(refs/vendors/microsoft/heads/main)] Update readme to refer to repo as mirror (#51)

[Eugene Rozenfeld]

https://gcc.gnu.org/g:aa004df2ff4b2d686f445115779662c004f2bafe

commit aa004df2ff4b2d686f445115779662c004f2bafe
Author: Victor Tong <53017530+vitong@users.noreply.github.com>
Date:   Fri May 7 12:05:08 2021 -0700

    Update readme to refer to repo as mirror (#51)
    
    This change cleans up our README file to reflect what we're intending to use the GitHub repo for

Diff:
---
 README.md | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/README.md b/README.md
index ea89b56b65f..769cc300291 100644
--- a/README.md
+++ b/README.md
@@ -1,21 +1,23 @@
 # microsoft/gcc
 
-This repository is a fork of the [GCC repository](https://gcc.gnu.org/git/gcc.git) for Microsoft internal scenarios. **Consumption of packages produced in this repo for any other scenario is not recommended or supported.**
+This repository is a mirror of the Microsoft vendor branches in the [GCC repository](https://gcc.gnu.org/git/gcc.git) and is intended specifically for Microsoft internal scenarios. **Consumption of packages produced in this repository for any other scenario is not recommended or supported.** For a list of mirrored branches, see [Mirrored Branches](#mirrored-branches).
 
-Integration from the upstream GCC repository will occur regularly. Changes made in this repository will be contributed back upstream through the [existing GCC contribution process](https://gcc.gnu.org/contribute.html). PR requests from the external community will not be accepted as this repository isn't meant to be another mechanism to check into the GCC repository.
+This repository also contains scripts and workflow YAML files to build and test GCC using GitHub Actions that can be used by others in the GCC community. See [Scripts and Workflows](#scripts-and-workflows) for more details.
 
-This repository also contains scripts and workflow YAML files to build and test GCC using GitHub Actions. See [Scripts and Workflows](#scripts-and-workflows) for more details.
+This repository is not meant to be another mechanism for GCC developers to check into the GCC repository. Pull requests from the external community will not be accepted. Microsoft developers will follow the [existing GCC contribution process](https://gcc.gnu.org/contribute.html) and will submit patches to the GCC repository. They will run testing in this GitHub repository to verify that Microsoft scenarios are still working. 
 
-## Active Branches: 
+We intend to work with the GCC community to integrate any changes we make in our vendor branches back upstream to the corresponding GCC release branches and master where appropriate.
+
+## Mirrored Branches: 
 
 | Branch | Status | Description |
 | --- | --- | --- |
-| current | [![current Status](https://github.com/microsoft/gcc/actions/workflows/build/badge.svg?branch=current)](https://github.com/microsoft/gcc/actions?query=workflow%3Abuild+branch%3Acurrent) | Points to the [master branch](https://gcc.gnu.org/git/?p=gcc.git;a=shortlog;h=refs/heads/master) in the upstream GCC repository. This will be updated regularly.
-| gcc-9.1.0 | [![gcc-9.1.0 Status](https://github.com/microsoft/gcc/actions/workflows/build/badge.svg?branch=gcc-9.1.0)](https://github.com/microsoft/gcc/actions?query=workflow%3Abuild+branch%3Agcc-9.1.0) | Points to [releases/gcc-9.1.0 tag](https://gcc.gnu.org/git/?p=gcc.git;a=shortlog;h=releases/gcc-9.1.0) in the upstream GCC repository.
+| current | [![current Status](https://github.com/microsoft/gcc/actions/workflows/build/badge.svg?branch=current)](https://github.com/microsoft/gcc/actions?query=workflow%3Abuild+branch%3Acurrent) | Mirrors the *vendors/microsoft/main branch* in the upstream GCC repository. That vendor branch is based off the [GCC master branch](https://gcc.gnu.org/git/?p=gcc.git;a=shortlog;h=refs/heads/master).
+| gcc-9.1.0 | [![gcc-9.1.0 Status](https://github.com/microsoft/gcc/actions/workflows/build/badge.svg?branch=gcc-9.1.0)](https://github.com/microsoft/gcc/actions?query=workflow%3Abuild+branch%3Agcc-9.1.0) | Mirrors the *vendors/microsoft/9.1.0 branch* in the upstream GCC repository. That vendor branch is based off the [releases/gcc-9.1.0 tag](https://gcc.gnu.org/git/?p=gcc.git;a=shortlog;h=releases/gcc-9.1.0).
 
 ## Scripts and Workflows:
 
-Scripts and YAML files under the [.github](.github) directory leverage GitHub Actions to build and test GCC in PR and CI builds. These are available for anyone to use ([released under an MIT license](.github/LICENSE.txt)). The host and target of the workflows is **x86_64-pc-linux-gnu**. Future improvements will come to build on more hosts for more targets.
+The scripts and YAML files under the [.github](.github) directory leverage GitHub Actions to build and test GCC in pull requests and continuous integration builds. These are available for anyone to use ([released under an MIT license](.github/LICENSE.txt)). The host and target of the workflows is **x86_64-pc-linux-gnu**. Future improvements will come to build on more hosts for more targets.
 
 | Workflow | Description |
 | --- | --- |
@@ -24,4 +26,3 @@ Scripts and YAML files under the [.github](.github) directory leverage GitHub Ac
 
 ## Releases:
 *For Microsoft internal scenarios consumption only. TBD with more details*
-