docs: use $ to denote a command for consistency with other product docs (#468)

website/content/docs/developing/building.mdx

@@ -14,10 +14,10 @@ Building Boundary from source requires:
 - [Docker](https://docs.docker.com/get-docker/) installed
 - Basic development environment (git, xcode if you're on Mac, etc)
 
-1. `git clone https://github.com/hashicorp/boundary` or if you're using SSH auth for
-   github, `git clone git@github.com:hashicorp/boundary`
-2. `cd boundary`
-3. `make dev`
+1. `$ git clone https://github.com/hashicorp/boundary` or if you're using SSH auth for
+   github, `$ git clone git@github.com:hashicorp/boundary`
+2. `$ cd boundary`
+3. `$ make dev`
 
 Once you've built Boundary, the binary will be available at `<repo path>/bin/boundary`. Move this
 binary to somewhere in your `$PATH` such as `/usr/local/bin`.
@@ -25,6 +25,6 @@ binary to somewhere in your `$PATH` such as `/usr/local/bin`.
 ## Cross Platform Build
 
 If you need to cross compile boundary for another OS or architecture, use the [XC_OSARCH](https://github.com/hashicorp/boundary/blob/master/scripts/build.sh#L26)
-environment variable to set this. Example: `XC_OSARCH=linux/amd64 make dev`
+environment variable to set this. Example: `$ XC_OSARCH=linux/amd64 make dev`
 
 For more details, please consult the [Boundary project on GitHub](https://github.com/hashicorp/boundary#build-and-start-boundary-in-dev-mode).