Improve SDR handbook

On https://about.gitlab.com/handbook/marketing/marketing-sales-development/sdr/ there are some typos and some ways we can improve the page.

• SAL = Service Level Agreement should be SLA = Service Level Agreement
• IQM = Initial Qualifying Meeting MQL = Marketo Qualified Lead - an inquiry that has been qualified through systematic means (e.g. through demographic/firmographic/behaviour lead scoring) should be two separate entries in the glossary:
  • IQM = Initial Qualifying Meeting
  • MQL = Marketo Qualified Lead - an inquiry that has been qualified through systematic means (e.g. through demographic/firmographic/behavior lead scoring)
• SAO = Sales Accepted Opportunity - an opportunity Sales agrees to pursue following an introductory meeting (Stage 1-Discovery) should be SAO = Sales Accepted Opportunity - an opportunity Sales agrees to pursue following an Initial Qualifying Meeting
• SCLAU = Abbreviation for SQO Count Large And Up. This is the number of opportunities in large and strategic organizations passed from marketing to sales. should read SCLAU = Abbreviation for SQO Count Large And Up.
• I-SDR = Inbound Sales Development Rep (FKA Inbound BDR) O-SDR = Outbound Sales Development Rep (FKA Outbound BDR) should be two separate entries in the glossary:
  • I-SDR = Inbound Sales Development Representative (FKA Inbound BDR)
  • SDR = Sales Development Rep (FKA Outbound BDR)
• SQL = Sales Qualified Lead - when Sales re-qualifies and has a meeting should be deprecated in favor of SQO
• SQO = Sales Qualified Opportunity - an opportuity where Sales has completed discovery and qualified (Stage 2-Scoping or later) should read SQO = Sales Qualified Opportunity - an opportunity that has past initial qualification and progressed into the sales pipeline (Stage 1-Discovery or later).
• TEDD = Technology, Engineering, Development and Design dataset from Discover.org should read TEDD = Technology, Engineering, Development and Design - Used to estimate the maximum potential users of GitLab within a company

Other thoughts to improve:

• This page should have a table of contents based on headers.
• The glossary should be at the end.
• There should be a section dedicated to covering the waterfall stages with a diagram showing how progression takes place, similar to https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiv2rrsqbrXAhVL72MKHd7rAR4QjRwIBw&url=https%3A%2F%2Flaurenondemand.com%2F2012%2F06%2F27%2Ftop-5-takeaways-from-siriusdecisions-summit-2012%2F&psig=AOvVaw2y5HzjOsfHN09NDzQ23RQZ&ust=1510620450043098 but using our stage names (use SDR-AL instead of TAL, and SDR-QL instead of TQL, SAO instead of SAL, and SQO instead of SQL).

@Nrflynn please open a MR to close this out and assign to me.

cc: @jjcordz @chetbackman @mollybeth