Enhance "A Warm Welcome to ASN.1 and DER"

• Add a table of contents to the top of the doc
• Add a table containing the bit value to constructed vs primitive
• Add boolean to Encoding of specific types. The Layman's Guide doesn't and I needed to figure it out today. I had to go back to X.690 (07/02).
• Clarify what the high bit vs low bits are.
• Add a picture/diagram explaining how to read parse a byte. Example:

Context Specific
| Context Specific
| | Primitive
| | | Encoded tag values
| | | |-------|
| | | |
8 7 6 5 4 3 2 1
1 0 0 0 0 0 0 1

= 129
which in hex is 0x81
and when looking at the CRL IssuerDistributionPoint flag onlyContainsUserCerts: 30038101FF

		RFC 5280 Section 5.2.5

		IssuingDistributionPoint ::= SEQUENCE {
			distributionPoint          [0] DistributionPointName OPTIONAL,
			onlyContainsUserCerts      [1] BOOLEAN DEFAULT FALSE,
			onlyContainsCACerts        [2] BOOLEAN DEFAULT FALSE,
			...
		}

I can tell that the onlyContainsUserCerts flag is set and nothing else is.

Open the “A Warm Welcome to ASN.1 and DER” article and review the linked constructed-versus-primitive, encoding, X.690, and RFC 5280 references. Add the requested table of contents, bit-value and BOOLEAN explanations, high-bit/low-bit clarification, and byte-reading diagram; done means each requested concept is clear in the published document.