added Devcontainer to building from source

BUILDING_FROM_SOURCE.md

@@ -2,6 +2,17 @@
 
 If you run into any problems getting Roc built from source, please ask for help in the `#beginners` channel on [Roc Zulip](https://roc.zulipchat.com) (the fastest way), or create an issue in this repo!
 
+## Using Devcontainer
+
+### Codespaces
+To access the browser-based editor, you can change the URL of your repository to https://github.dev/roc-lang/roc, replacing github.com with github.dev or go to the roc repo on https://github.com/roc-lang/roc and press . (period key).
+
+Or use it locally in [VSCode](https://code.visualstudio.com/docs/remote/codespaces)
+
+### Docker
+
+Or even run it in your local Docker environment [Developing inside a Container](https://code.visualstudio.com/docs/devcontainers/containers)
+
 ## Using Nix
 
 On MacOS and Linux, we highly recommend Using [nix](https://nixos.org/download.html) to quickly install all dependencies necessary to build roc.
@@ -140,7 +151,7 @@ To use the `repl` subcommand, execute `cargo run repl`.
 
 The default is a developer build. For an optimized build, use:
 
-```
+```sh
 cargo build --release --bin roc
 ```
 

devtools/signing.md

@@ -28,7 +28,7 @@ Without a Yubikey:
 This explanation was based on the steps outlined [here](https://scatteredcode.net/signing-git-commits-using-yubikey-on-windows/).
 
 On linux, run:
-```
+```sh
 gpg --list-keys --keyid-format SHORT | grep ^pub
 gpg --export --armor [Your_Key_ID] > public.asc
 ```
@@ -46,19 +46,19 @@ Install the [YubiKey Minidriver for 64-bit systems – Windows Installer](https:
 Insert your Yubikey and check if it is mentioned in the output of `gpg --card-status` (powershell).
 
 Open powershell and execute:
-```
+```sh
 git config --global gpg.program "c:\Program Files (x86)\GnuPG\bin\gpg.exe"
 git config --global commit.gpgsign true
 gpg --list-secret-keys --keyid-format LONG
 ```
 The last command will show your keyid. On the line that says `[SC]`, copy the id.
 In the example below the id is 683AB68D867FEB5C
-```
+```sh
 sec>  rsa4096/683AB68D867FEB5C 2020-02-02 [SC] [expires: 2022-02-02]
 ```
 
 Tell git your keyid:
-```
+```sh
 >git config --global user.signingkey YOUR_KEY_ID_HERE
 ```