Instruction for building 1.7.21 release

(cherry picked from commit e02395f)

docs/building/build-1.7.20.md

@@ -40,7 +40,8 @@ docker run --rm -it --name kotlin-build-$DEPLOY_VERSION \
 
 This generates a ZIP file: `dist/kotlin-compiler-1.7.20.zip`.
 
-Check that the SHA 256 checksum is the same as the ZIP file [published on GitHub](https://github.com/JetBrains/kotlin/releases/download/v1.7.20/kotlin-compiler-1.7.20.zip): 5e3c8d0f965410ff12e90d6f8dc5df2fc09fd595a684d514616851ce7e94ae7d
+Check that the SHA 256 checksum is the same as the ZIP file [published on GitHub](https://github.com/JetBrains/kotlin/releases/download/v1.7.20/kotlin-compiler-1.7.20.zip):
+5e3c8d0f965410ff12e90d6f8dc5df2fc09fd595a684d514616851ce7e94ae7d
 
 ## Build maven artifacts
 

docs/building/build-1.7.21.md

@@ -0,0 +1,60 @@
+# Building 1.7.21
+
+This tutorial explains how to build release [1.7.21](https://github.com/JetBrains/kotlin/releases/tag/v1.7.21) locally.
+
+## Prerequisites
+You must have:
+* Linux or MacOS.
+* Docker installed.
+* 14 GB memory available and configured in Docker. 
+
+## Set environment variables
+
+The following environment variables must be set:
+
+```
+export DEPLOY_VERSION=1.7.21
+export BUILD_NUMBER=1.7.21-release-272
+export KOTLIN_NATIVE_VERSION=1.7.21
+export DOCKER_CONTAINER_URL=kotlin.registry.jetbrains.space/p/kotlin/containers/kotlin-build-env:v5
+```
+## Clone Kotlin repository
+
+In a new folder, clone the release tag from the Kotlin repository, and change directory to the build folder:
+
+```
+git clone --depth 1 --branch v$DEPLOY_VERSION https://github.com/JetBrains/kotlin.git kotlin-build-$DEPLOY_VERSION
+cd kotlin-build-$DEPLOY_VERSION
+```
+
+## Build and verify the compiler
+
+Download and save [scripts/build-kotlin-compiler.sh](https://github.com/JetBrains/kotlin/blob/1.7.20/scripts/build-kotlin-compiler.sh) to 
+the`scripts` folder in your repository, and then execute it in a docker container:
+
+```
+docker run --rm -it --name kotlin-build-$DEPLOY_VERSION \
+  --workdir="/repo" --volume="$(pwd):/repo" $DOCKER_CONTAINER_URL \
+  /bin/bash -c "./scripts/build-kotlin-compiler.sh $DEPLOY_VERSION $BUILD_NUMBER"
+```
+
+This generates a ZIP file: `dist/kotlin-compiler-1.7.21.zip`.
+
+Check that the SHA 256 checksum is the same as the ZIP file [published on GitHub](https://github.com/JetBrains/kotlin/releases/download/v1.7.21/kotlin-compiler-1.7.21.zip):
+8412b31b808755f0c0d336dbb8c8443fa239bf32ddb3cdb81b305b25f0ad279e
+
+## Build maven artifacts
+
+Download and save [scripts/build-kotlin-maven.sh](https://github.com/JetBrains/kotlin/blob/1.7.20/scripts/build-kotlin-maven.sh) to 
+the `scripts` folder in your repository, and then execute it in a docker container:
+
+```
+docker run --rm -it --name kotlin-build-$DEPLOY_VERSION \
+  --workdir="/repo" --volume="$(pwd):/repo" $DOCKER_CONTAINER_URL \
+  /bin/bash -c "./scripts/build-kotlin-maven.sh $DEPLOY_VERSION $BUILD_NUMBER $KOTLIN_NATIVE_VERSION"
+```
+
+This generates a ZIP file: `build/repo-reproducible/reproducible-maven-1.7.21.zip`.
+
+**Note:** Instructions for checking reproducibility will be covered in the upcoming release. There are already many JAR files on Maven
+central that are reproducible with this tutorial.

docs/building/index.md

@@ -1,3 +1,4 @@
 # Kotlin builds
 
-* [1.7.20 Release](build-1.7.20.md)
+* [1.7.20 Release](build-1.7.20.md)
+* [1.7.21 Release](build-1.7.21.md)