Use main branch in documentation

Signed-off-by: John Pugliesi <jpugliesi12@gmail.com>

README.md

@@ -46,12 +46,12 @@ Install this library in your own project with [jsonnet-bundler](https://github.c
 $ mkdir my-kube-thanos; cd my-kube-thanos
 $ jb init  # Creates the initial/empty `jsonnetfile.json`
 # Install the kube-thanos dependency
-$ jb install github.com/thanos-io/kube-thanos/jsonnet/kube-thanos@master # Creates `vendor/` & `jsonnetfile.lock.json`, and fills in `jsonnetfile.json`
+$ jb install github.com/thanos-io/kube-thanos/jsonnet/kube-thanos@main # Creates `vendor/` & `jsonnetfile.lock.json`, and fills in `jsonnetfile.json`
 ```
 
 > `jb` can be installed with `go get github.com/jsonnet-bundler/jsonnet-bundler/cmd/jb`
 
-> An e.g. of how to install a given version of this library: `jb install github.com/thanos-io/kube-thanos/jsonnet/kube-thanos@master`
+> An e.g. of how to install a given version of this library: `jb install github.com/thanos-io/kube-thanos/jsonnet/kube-thanos@main`
 
 In order to update the kube-thanos dependency, simply use the jsonnet-bundler update functionality:
 ```shell

jsonnet/thanos-mixin/README.md

@@ -2,4 +2,4 @@
 
 > ### `thanos-mixin` is **moved** to the upstream [`Thanos`](https://github.com/thanos-io/thanos) repository.
 
-Please visit [`thanos/mixin/thanos`](https://github.com/thanos-io/thanos/blob/master/mixin/README.md) for further instructions.
+Please visit [`thanos/mixin/thanos`](https://github.com/thanos-io/thanos/blob/main/mixin/README.md) for further instructions.