Add info about related projects to readme

Since the trace viewer depends on code from several other repos,
resolving issues sometimes requires making changes in these related code
bases. At the moment, the main link to these other projects is
in the repo issue label descriptions (not the first place a new
contributor would look) and there are no links to where to find the code
for these related projects. It is challenging to find these related
projects unless you already know the project architecture.

Adding context about related projects (and where to find their code) to
the readme makes this information more accessible and reduces the
onboarding effort for new contributors.

Signed-off-by: Erica Bugden <erica.bugden@gmail.com>

README.md

@@ -158,3 +158,14 @@ Currently, the **Time Graph Tooltip** is populated when selecting a state in a T
 * [_Sign-off:_](https://git-scm.com/docs/git-commit#Documentation/git-commit.txt---signoff) Use your full name and a long-term email address. This certifies that you have written the code and that, from a licensing perspective, the code is appropriate for use in open-source.   
 * [How to format the message](https://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html)
 
+## Related code
+This trace viewer depends on code from several other repos. Sometimes resolving issues in the trace viewer repo requires making changes in these code bases:
+
+| Project | Description | Related issues  | Links |
+|---------------|----|--------------------------|---|
+| [Theia](https://theia-ide.org/) | Theia is a framework for making custom IDEs. It provides reusable components (ex. Text editor, terminal, etc.) and is extensible. For example, this trace viewer is an extension for Theia-based IDEs. | | [Code](https://github.com/eclipse-theia/theia), [Ecosystem](https://github.com/theia-ide) |
+| [Trace Compass](https://www.eclipse.org/tracecompass/) | Trace analysis tool and precursor to this trace viewer. | [label:"Trace Compass"](https://github.com/theia-ide/theia-trace-extension/labels/Trace%20Compass) | [Dev info](https://wiki.eclipse.org/Trace_Compass), [Dev setup](https://wiki.eclipse.org/Trace_Compass/Development_Environment_Setup) |
+| [Trace Compass Server](https://download.eclipse.org/tracecompass.incubator/trace-server/rcp/?d) | A reference implementation of a Trace Server. Manages and analyzes trace files and provides this data to the trace viewer over the [Trace Server Protocol (TSP)](https://github.com/theia-ide/trace-server-protocol). This Trace Server implementation was originally part of Trace Compass so it requires the same dev setup. Because a protocol is used for communication (TSP), it is possible to develop alternative Trace Servers that are independent of Trace Compass. | [label:"Trace Server"](https://github.com/theia-ide/theia-trace-extension/labels/Trace%20Server) | [Dev setup](https://wiki.eclipse.org/Trace_Compass/Development_Environment_Setup) (same as Trace Compass), [Code](https://git.eclipse.org/r/admin/repos/tracecompass.incubator/org.eclipse.tracecompass.incubator) (same repo as Trace Compass incubator) |
+| [Trace Server Protocol (TSP)](https://github.com/theia-ide/trace-server-protocol) | Protocol used by the trace viewer to communicate with the trace server. | [label:"trace server protocol"](https://github.com/theia-ide/theia-trace-extension/labels/trace%20server%20protocol) |
+| [Client-side Trace Server Protocol implementation](https://github.com/theia-ide/tsp-typescript-client) | A client-side implementation of the Trace Server Protocol. Allows the trace viewer to communicate with the server. |  |   |
+| [Timeline Chart](https://github.com/theia-ide/timeline-chart) | Implements the Gantt charts used in this trace viewer.  | [label:timeline-chart](https://github.com/theia-ide/theia-trace-extension/labels/timeline-chart) |   |