[#674] Add summary page describing available TCR variants

variants-doc/tcr_variants.md

@@ -0,0 +1,45 @@
+# TCR Variants
+
+TCR tool can run several variants of TCR, as described in
+[this blog post](https://medium.com/@tdeniffel/tcr-variants-test-commit-revert-bf6bd84b17d3)
+by Thomas Deniffel.
+
+We encourage you to read through Thomas's blog post for a deeper understanding of how these
+variants differ and what each of them can bring.
+
+The selection of which variant TCR will be applying is done at launch time through
+TCR's tool `--variant` (or `-r`) command-line option.
+
+The variants currently supported by TCR tool are the following:
+
+- The Original
+- BTCR
+- The Relaxed (default)
+
+The state diagrams below summarize the behavior of each variant.
+
+## The Original
+
+```shell
+tcr --variant=original
+```
+
+![TCR Original variant](./variant-original.png)
+
+## BTCR - Build && Test && Commit || Revert
+
+```shell
+tcr --variant=btcr
+```
+
+![TCR BTCR variant](./variant-btcr.png)
+
+## The Relaxed
+
+```shell
+tcr --variant=relaxed
+```
+
+The above option `--variant=relaxed` may be omitted as this is the default variant.
+
+![TCR Relaxed variant](./variant-relaxed.png)