Manual: add 80 column line break suggestion.

Also:
- rework most of the language in the Introduction
- move note about special characters in pkgname or version
- note restrictions to version field are caused partly by xbps-checkvers
- fix indentation of 'maintainer' item

Manual.md

@@ -76,17 +76,19 @@ packages for XBPS, the `Void Linux` native packaging system.
 <a id="Introduction"></a>
 ## Introduction
 
-The `void-packages` repository contains all `source` packages that are the
+The `void-packages` repository contains all the
-recipes to download, compile and build binary packages for `Void`.
+recipes to download, compile and build binary packages for Void Linux.
-Those `source` package files are called `templates`.
+These `source` package files are called `templates`.
 
-The `template files` are `GNU bash` shell scripts that must define some required/optional
+The `template` files are shell scripts that define `variables` and `functions`
-`variables` and `functions` that are processed by `xbps-src` (the package builder)
+to be processed by `xbps-src`, the package builder, to generate binary packages.
-to generate the resulting binary packages.
+The shell used by `xbps-src` is GNU bash; `xbps-src` doesn't aim to be
+compatible with POSIX `sh`.
 
-By convention, all templates start with a comment briefly explaining what they
+By convention, all templates start with a comment saying that it is a
-are. In addition, pkgname and version can't have any characters in them that
+`template file` for a certain package. Most of the lines should be kept under 80
-would require them to be quoted, so they are not quoted.
+columns; variables that list many values can be split into new lines, with the
+continuation in the next line indented by one space.
 
 A simple `template` example is as follows:
 
@@ -447,10 +449,9 @@ Multiple licenses should be separated by commas, Example: `GPL-3.0-or-later, cus
   Note: `MIT`, `BSD`, `ISC` and custom licenses
   require the license file to be supplied with the binary package.
 
-- `maintainer` A string in the form of `name <user@domain>`.  The
+- `maintainer` A string in the form of `name <user@domain>`.  The email for this field
-  email for this field must be a valid email that you can be reached
+must be a valid email that you can be reached at. Packages using
-  at.  Packages using `users.noreply.github.com` emails will not be
+`users.noreply.github.com` emails will not be accepted.
-  accepted.
 
 - `pkgname` A string with the package name, matching `srcpkgs/<pkgname>`.
 
@@ -461,7 +462,12 @@ the generated `binary packages` have been modified.
 - `short_desc` A string with a brief description for this package. Max 72 chars.
 
 - `version` A string with the package version. Must not contain dashes or underscore
-and at least one digit is required. Shell's variable substition usage is not allowed.
+and at least one digit is required. Using bash's pattern substitution and prefix and
+suffix matching isn't supported, since this field needs to be parsed by
+`xbps-checkvers(1)`. Using variables in this field should be avoided.
+
+Neither `pkgname` or `version` should contain special characters which make it
+necessary to quote them, so they shouldn't be quoted in the template.
 
 <a id="optional_vars"></a>
 #### Optional variables