Fix caps and highlighted embedded code where possible

Optional.md

@@ -1,4 +1,4 @@
-## Optional Checks
+## Optional checks
 
 ShellCheck supports additional checks that are not enabled by default. These are generally subjective or stylistic.
 
@@ -6,7 +6,7 @@ ShellCheck supports additional checks that are not enabled by default. These are
 
 Checks can be enabled with flags or an `enable` [[directive]] in the file or `.shellcheckrc`:
 
-```
+```sh
 #!/bin/sh
 # shellcheck enable=require-variable-braces
 echo "$RANDOM"  # Will emit a suggestion to use `${RANDOM}`
@@ -14,7 +14,11 @@ echo "$RANDOM"  # Will emit a suggestion to use `${RANDOM}`
 
 or put `enable=require-variable-braces` in a `.shellcheckrc` in your home directory or project root.
 
-They can also be enabled on the command line with `shellcheck -o require-variable-braces myscript`
+They can also be enabled on the command-line with `-o`:
+
+```console
+$ shellcheck -o require-variable-braces myscript
+```
 
 
 ### Enabling all checks
@@ -29,7 +33,8 @@ However, if you for debugging or evaluation purposes want to see what's availabl
 To see which checks are available in your version of ShellCheck, use the `--list-optional` flag.
 
 Optional checks as of version 0.8.0:
-```
+
+```console
 $ shellcheck --list-optional
 
 name:    add-default-case