Docs page for "using Sourcegraph with a monorepo"

Created by: dadlerj

See: https://sourcegraph.slack.com/archives/C0B2RU51Q/p1581615419427200

We have had a number of calls with prospects and customers recently in which they expressed uncertainty as to whether Sourcegraph would solve their needs, given they operate out of "huge" monorepos (though the size and complexity varies widely). This list includes:

• https://app.hubspot.com/contacts/2762526/company/554275594
• https://app.hubspot.com/contacts/2762526/company/768958891
• https://app.hubspot.com/contacts/2762526/company/1749284051
• https://app.hubspot.com/contacts/2762526/company/815026279
• https://app.hubspot.com/contacts/2762526/company/416674538
• https://app.hubspot.com/contacts/2762526/company/557691596

As well as some existing customers who have to deal with this:

• https://app.hubspot.com/contacts/2762526/company/947819054
• https://app.hubspot.com/contacts/2762526/company/578600789
• https://app.hubspot.com/contacts/2762526/company/555146901
• etc...

Examples of questions we get include:

• High-level use cases for Sourcegraph when using a monorepo
• General scale/performance concerns (for search and code intelligence)
• Usage of Sourcegraph with git submodules or sub-trees (how do these appear in the UI/in searches?)
• Custom git binaries, or usage of Sourcegraph with tools like git-meta
• Massive numbers of branches
• UI tweaks (e.g., "can we customize the search scopes to show submodules or branches instead of repos?")
• Etc.

Searching our docs for "monorepo" or "monolith" or "submodule" doesn't return anything useful on this topic.

Happy to answer any questions about this ask!