doc: please document that zig do not accept '\t' in the source code file

[bronze1man]

I just want to write something and i come across this problem.

The document do not say anything about it.

#544

xxx/h.zig:12:1: error: invalid character: '\t'
        return std.io.getStdOut();
^

For some discussion on the rationale behind these design decisions, see issue #663

[nodefish]

It's mentioned here: https://ziglang.org/documentation/master/#Source-Encoding

Throughout all zig source code (including in comments), some codepoints are never allowed:

• Ascii control characters, except for U+000a (LF): U+0000 - U+0009, U+000b - U+0001f, U+007f. (Note that Windows line endings (CRLF) are not allowed, and hard tabs are not allowed.)

• Non-Ascii Unicode line endings: U+0085 (NEL), U+2028 (LS), U+2029 (PS).