perf-metrics.md: Add performance metrics

Add performance metrics data from Phase-1
to the repo.

Closes #10

Author: ksdme

docs/images/perf-phase-1.png

@@ -0,0 +1,51 @@
+## Performance Metrics
+
+Performance metrics of the coala-ls server. To maintain standard
+comparison against some configuration at every phase of development
+the codebase from https://github.com/ksdme/projects/tree/coalals-perf
+is used to calculate the metrics. The .coafile configuration can be
+found in the same repo.
+
+Metrics are calculated on a per file basis since such said metrics
+are heavily dependent on the source file and the coala configuration.
+The number of concurrent jobs also affects the performance heavily,
+metrics are also collected as per the number of jobs running. The
+average time for the server to start up is `3.2 Sec`.
+
+Response times for various requests in seconds sent to the server
+with `max_jobs = 1`.
+
+| request type                                 | time      | time (legacy) |
+| -------------------------------------------- | --------- | ------------- |
+| initialize                                   | 0.03 sec  | 0.019 sec     |
+| `resources/css/404.css` textDocument/didOpen | 7.18 sec  |               |
+| `resources/css/404.css` textDocument/didSave | 5.32 sec  | 11.36 sec     |
+| `index.html` textDocument/didOpen            | 10.16 sec |               |
+| `index.html` textDocument/didSave            | 8.33 sec  | 10.95 sec     |
+
+
+Response time metrics in seconds with `max_jobs = 2`. coala-vs-code does
+not support any other modes other than a default `max_jobs = 1` equivalent.
+
+| job | request type                                 | time      |
+| --- | -------------------------------------------- | --------- |
+|     | initialize                                   | 0.03 sec  |
+| J1  | `resources/css/404.css` textDocument/didOpen | 11.03 sec |
+| J1  | `index.html` textDocument/didOpen            | 15.65 sec |
+| J2  | `resources/css/404.css` textDocument/didSave | 5.08 sec  |
+| J2  | `index.html` textDocument/didSave            | 8.40 sec  |
+
+
+Response time metrics in seconds with `max_jobs = 3`.
+
+| job | request type                                        | time     |
+| --- | --------------------------------------------------- | -------- |
+|     | initialize                                          | 0.03 sec |
+| J1  | `resources/css/404.css` textDocument/didSave        | 5.15 sec |
+| J1  | `index.html` textDocument/didOpen                   | 8.45 sec |
+| J2  | `resources/css/404.css` textDocument/didSave        | 5.12 sec |
+| J2  | `resources/css/style.css` textDocument/didSave      | 4.57 sec |
+| J2  | `index.html` textDocument/didSave                   | 8.65 sec |
+
+### Graphical Representation
+![Graph](./docs/images/perf-phase-1.png)