Document how to add new languages to plugin.

README.md

@@ -98,7 +98,9 @@ For NeoVim with `init.lua`:
 vim.g.licenser_author = "Your Name"
 ```
 
-### Supported Licenses
+### Licenses
+
+#### Supported Licenses
 
 vim-licenser includes templates for the following licenses:
 
@@ -118,7 +120,17 @@ vim-licenser includes templates for the following licenses:
 
 Use tab completion to see all available licenses: `:Licenser <TAB>`
 
-### Supported File Types
+#### Adding New Licenses
+
+To add a new license, create a new file in the `licenses` directory with the
+name of the license (e.g., `MIT.txt`) and add the license text to the file. The
+license text can contain the YEAR and AUTHOR placeholders, which will be
+replaced with the current year and the author name when the license header is
+added to the source file.
+
+### File Types
+
+#### Supported File Types
 
 vim-licenser automatically detects your file type and applies the appropriate
 comment style. Supported file types include:
@@ -128,13 +140,24 @@ shell, sql, swift, typescript, typescriptreact, vim, xml, yaml
 
 For more information, see `:help licenser` after installation.
 
-## Adding New Licenses
+#### Adding Support for New File Types
 
-To add a new license, create a new file in the `licenses` directory with the
-name of the license (e.g., `MIT.txt`) and add the license text to the file. The
-license text can contain the YEAR and AUTHOR placeholders, which will be
-replaced with the current year and the author name when the license header is
-added to the source file.
+To add support for a new file type, add an entry to the `comment_styles`
+dictionary in the `plugin/licenser.vim` file. The key should be the file type
+as recognized by Vim/NeoVim, and the contents should be as follows:
+
+- `margin`: If the prefix and suffix should be used on their own lines. E.g. in
+  C and C++ the comment style is `/* */`, so the margin should be set to `1`.
+  In Python, the comment style is `#`, so the margin should be set to `0`.
+- `hashbang`: If the file type supports shebang a line (e.g., `#!/usr/bin/env
+  python3`), set this to `1`. Otherwise, set it to `0`. This is used to
+  determine if the license header should be added after the shebang line.
+- `prefix`: Comment string to use on the first line. Unused if `margin` is set
+  to `0`.
+- `middle`: Comment string to use on the middle lines. If `margin` is set to
+  `0`, this will be used on all lines.
+- `suffix`: Comment string to use on the last line. Unused if `margin` is set to
+  `0`.
 
 ## License